`85.0.0` ➡️ `85.1.0`

⚠️ The biggest change in this PR by far is the **removal** of several
`EuiFilterSelectItem` CSS classes and styles associated with those
classes. EUI has previously exported component-specific CSS classes for
usage such as `.euiFilterSelect__items`,
`.euiFilterGroup__popoverPanel`, or `.euiAccordionForm`.

❌ **As of our move to CSS-in-JS, we are actively moving away from this
architecture**. The goal is to either provide either a component or prop
directly to you instead of a CSS class. As a reminder, our classNames
are not guaranteed APIs and are subject to change without warning -
should you need to tweak or customize EUI's styling, we strongly
recommend passing in your own `className`.

💬 Moving forward, EUI will attempted to convert any usages of removed
CSS classes and their direct usages in Kibana for you. In most cases,
we'll hopefully be able to take the correct path of using a component or
prop instead. In cases where we cannot or significant/complex changes
are required, we may temporarily convert the CSS to a static CSS-in-JS
usage instead and add a TODO asking the relevant team to address this in
their own time (for example, the deprecation of `EuiFilterSelectItem`
and its conversion to `EuiSelectable`).

## [`85.1.0`](https://github.com/elastic/eui/tree/v85.1.0)

- Updated `EuiComboBox`'s `options` to accept `option.append` and
`option.prepend` props
([#6953](elastic/eui#6953))
- Updated deprecated `.substr()` usages to `.substring()`
([#6954](elastic/eui#6954))
- Updated `EuiInlineEdit`'s read mode button to include a title tooltip,
increasing readability of truncated text
([#6966](elastic/eui#6966))

**Bug fixes**

- Fixed `EuiFilterGroup`'s responsive styles
([#6983](elastic/eui#6983))

**Deprecations**

- Deprecated `EuiFilterSelectItem`; Use `EuiSelectable` instead
([#6982](elastic/eui#6982))

**CSS-in-JS conversions**

- Converted `EuiFilterSelectItem` to Emotion
([#6982](elastic/eui#6982))
- Removed `.euiFilterSelect__items` CSS; Use `EuiSelectable` instead
([#6982](elastic/eui#6982))
- Removed `.euiFilterSelect__note` and `.euiFilterSelect__noteContent`
CSS; Use `EuiSelectableMessage` instead
([#6982](elastic/eui#6982))
- Added `focus.transparency` and `focus.backgroundColor` theme tokens
([#6984](elastic/eui#6984))

---------

Co-authored-by: Cee Chen <constance.chen@elastic.co>
Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>