* Calculate savings per swap relative to median values

* Update test mock quotes, add getMedian tests

* Identify assets by sourceToken and destinationToken

The MetaMask fee is shown with two percent signs on the view quote page, because the percent sign is embedded in the fee amount as well as in the localized message.

The fee amount used now comes from the API, and does not have a percent sign. The percent sign is now only in the localized message. This allows for different locales to display the percentage differently. The old hard-coded value with a percent sign embedded has been removed, as it is no longer used anywhere.

On Windows, spawn fails if the exact filename
of a binary isn't passed. e.g. `spawn('yarn')` fails
because the binary is named `yarn.cmd`.
Instead, we depend on `cross-spawn` which handles differences
in `spawn` across platforms.

The `metaMaskFee` property on the "quote data" PropType was not used,
and it never existed in practice. This resulted in PropType errors.

The non-existent property has been removed.

This parameter to the `quotesToRenderableData` function was never
passed in. It has been removed.

The `AwaitingSwap` component was emitting a React warning when rendered
because a component was being rendered in an array without having a
`key` prop set.

A key has been added to the `CountdownTimer` component, which is passed
into the translation helper in an array. The warning no longer appears.

The `message` prop of `ActionableMessage` had a PropType of `string`,
but it was being passed a `node`. This was resulting in a PropType
error in the console on the view quote page.

The PropType has been changed to `node`, and the error is now gone.

The `InfoTooltip` component had a `contentText` prop with a PropType of
`string` that was being passed a `node` as of #9614. This resulted in a
PropType error.

The `contentText` prop was being passed directly to `Tooltip` component
as the prop `html`, which has a PropType of `node`. A string is a valid
`node` type, which is why this worked before.

The `contentText` prop is now of type `node`, and the error no longer
appears.

The `conversionRate` prop of `GasModalPageContainer` was updated
recently in PR #9623 to have a PropType of `string` instead of
`number`. This resulted in a PropType error whenever this modal was
rendered, as `conversionRate` is always a `number`.

The PropType has been reverted to the correct type, `number`.

This change removes an incorrect comment about migrations

Fix 9638 - Prevent excessive overflow from swap dropdowns

Sorting was broken for the "Quote Source" column of the quote sort
list. Attempting to sort by this column would arrange the quotes in a
seemingly random order.

It appears that this was due to this column being programmed to sort by
a property called `liquiditySource`, which does not exist in the quote
data. I'm unsure what the difference between `liquiditySource` and
`quoteSource` was supposed to be; the values in the mocks are all
identical.

All references to `liquiditySource` have been updated to refer to
`quoteSource` instead, and the sorting now works correctly.

This change updates the command used to create RC pull requests to create [draft PRs][1].

  [1]:https://docs.github.com/en/free-pro-team@latest/github/collaborating-with-issues-and-pull-requests/about-pull-requests#draft-pull-requests

Make loading screen more concise

`@metamask/eslint-config` has been updated to v4.1.0. This update
requires that we update `eslint` to v7 as well, which in turn requires
updating most `eslint`-related packages.

Most notably, `babel-eslint` was replaced with `@babel/eslint-parser`,
and `babel-eslint-plugin` was replaced by `@babel/eslint-plugin`. This
required renaming all the `babel/*` rules to `@babel/*`.

Most new or updated rules that resulted in lint errors have been
temporarily disabled. They will be fixed and re-enabled in subsequent
PRs.

Refs #9663

See [`node/no-callback-literal`][1] for more information.

This change enables `node/no-callback-literal` and fixes the issues raised by the rule.

  [1]:https://github.com/mysticatea/eslint-plugin-node/blob/v11.1.0/docs/rules/no-callback-literal.md

Consolidates the background and UI segment implementations into a shared solution.

This results in the introduction of our first shared module.

Co-authored-by: Erik Marks <25517051+rekmarks@users.noreply.github.com>

Refs #9663

See [`node/no-path-concat`][1] for more information.

This change enables `node/no-path-concat` and fixes the issues raised by the rule.

  [1]:https://github.com/mysticatea/eslint-plugin-node/blob/v11.1.0/docs/rules/no-path-concat.md

Our ENS resolver for the browser address bar was incorrectly resolving
addresses that included query strings. We were concatenating the `path`
property with the `search` property, despite the fact that the `path`
property already contains `search`. As a result, `search` was
duplicated in the resolved addresses.

For example, if an IPFS content ID was found for this address, the
resolved address for `metamask.eth/?foo=bar` would have the path
`/?foo=bar?foo=bar`

The original intent was likely to use `pathname` in place of `path`.
The resolver has been updated to use `pathname`, and the query string
now appears only once in the resolved address.

Refs #9663

See [`node/no-deprecated-api`][1] for more information.

This change enables `node/no-deprecated-api` and fixes the issues raised by the rule.

  [1]:https://github.com/mysticatea/eslint-plugin-node/blob/v11.1.0/docs/rules/no-deprecated-api.md

The change to the way that `punycode` is imported is to address the fact that
third-party module is hidden by the built-in. This is a silly hack but it works.

This will allow usage in areas where getting the line-height, etc
of the typography settings will introduce issues. The mixins have been
updated to references these variables so that they can be changed in
one place in the future

This reverts commit 5456d55.

The v8.1.3 changelog has been updated with all user-facing changes
included with v8.1.3

PR #9612 was left under "Current Develop Branch" because it has been
temporarily reverted for this release. It was added there now so that
we don't forget about it, as the revert might result in that commit
not being populated by the changelog script for the next release.

Three new more user-facing changes were added to the release branch.