this pr adds the `key` and `ref` fields as optional onto the `slot`
element's typings. it also performs some minor refactoring to make
better reuse of typings.

add ionitron holiday triage message

fix `indexOf` call for the step attribute to look for the correct
attribute name.

hoist the check for `value` attribute to exit early if the attribute
does not exist, avoiding unneeded lookups of other attributes

STENCIL-79: Fix typo on <input> attribute validations

update prettier to the latest available version of the library, v2.5.1.
continue to use exact version in package.json to prevent accidental
formatting regressions/differences between users

This reverts commit 4a5da0f (#3187) 
to end the 2020 holiday triage season

this commit updates the prettier ignore configuration to use globs for
the `dist` and `www` directories under the root `test/` directory. this
prevents files in the `test/end-to-end` directory (and others) from
being formatted

remove `test/browser-compile` to ensure src files are properly
formatted. the test output for this directory is covered by the new
globs

Replicate some of the work (read: a lot) of the work done in ionic-team/ionic-framework#24368. Highlights include:
- adding the Stencil logo
- adding quick links to things like documentation, the community
- removing redundant/out of date information
- removing data that can be found in the Stencil docs

designate the volta adr as accepted and that volta is an official part
of our development toolchain. this comes after a month of using volta
with no major issues in the codebase.

this commit adds JSDoc to a portion of Stencil's logging infrastructure.
it was motivated by a spike wherein investigating adding error codes to
the compiler were explored. this work is recovered from that effort, to
help aid in understanability of this portion of the codebase.

some methods have been renamed to better reflect their intent.

some usages of `var` have been converted to `let`, as usage of the
variable defined using `var` did not appear to need to be declared using
the keyword

run `npm audit fix --only=dev` within the `test/karma`
directory. a good deal of the security vulnerabilities that GitHub warns
us about are in this directory, and many can be fixed (assuming packages
follow semver) with a quick audit+fix

upgrade webpack-cli to v4 from v3 to resolve security issue found in
v3. there appears to be only one breaking change in v4 (`--plugin` is 
removed) and it does not affect us since stencil uses this cli in such a
limited capacity

remove unused plugins rollup-plugin-node-builtins,
rollup-plugin-node-globals, jasmine-core

install karma-jasmine v4. the only breaking change is v4 drops node 8
support and adds node 14 support, which does not apply to this section
of the codebase

upgrade karma-typescript package

this commit restores running the `npm test` command as a part of the
root level package.json's `test.end-to-end` script (and readds it to
CI).

this commit provides support for jest 27 in stencil. this is
accomplished by no longer pulling default options from the jest-cli
package, which now encapsulates its contents through an `exports` field
in its package.json file. during the course of this work, it was
discovered the same fields/defaults were used with Jest 24, 25, & 26.
Those options have been pulled out into a helper function to be provided
for Jest v24 thru 27 to ensure a consistent experience. this helper will
be removed in a future version of Stencil.

the test runner for consumers is locked to jest-jasmine2 for backwards
compatibility in this commit.

jest-runner exposes its default export differently in jest 27. the
creation of a stencil test runner has been updated to handle the
differences between jest v27 and v26 (and under).

jest, jest-cli, jest-environment-node were all updated to the latest
patch version to test with the latest and greatest versions of the
libraries.

update @types/jest to v27, set as recommended version 

add an adr for jest 27 work

this commit adds a simplistic implementation of composedPath.
specifically, it inspects a MockEvent's target, and attempts to
climb the dom to provide the path the event propagates. this
implementation does not take into account closed shadow roots, nor
slots. the reason for which is that unlike a browser, which has far more
knowledge of the dom and event phases, stencil has none of this at the
mock-doc level, making a deep implementation difficult. a fuller
featured version may be considered for a future version of stencil

STENCIL-240: Enhance MockEvent to support composedPath()