Fix first focus determination. (flutter#33279)

Replacing the algorithm for finding the first focusable item in the focus tree. Somehow it was a kind of gibberish before, and really didn't work or make sense.

Add macosPrefix to the pubspec schema for plugins (flutter#33287)

Adds a new macosPrefix, which serves the same purpose as iosPrefix but
for macOS plugins.

It is not yet used by the tooling, but this allows for plugins to start
to be written using it in preparation for tooling support for plugins.

Part of flutter#32718

Slight clarification in the ImageCache docs (flutter#33195)

It was easy to miss the reference to the top-level `imageCache`
property before.  This calls out the property a little more
explicitly.

303a391 fix dartdevc build (flutter/engine#9036) (flutter#33155)

flutter/engine@75963db...303a391

git log 75963db..303a391 --no-merges --oneline
303a391 fix dartdevc build (flutter/engine#9036)

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Update enabled color for outlined text fields. (flutter#33083)

Resets the enabled color for outline text field default borders to "On Surface 38%" instead of "On Surface 12%" to match spec. Also fixes the hover overlay to be "On Surface 12%" to match spec.

Fix needsCompositing propagation from child widgets. (flutter#32717)

This fixes propagation of needsCompositing from child widgets.

When needsCompositing is turned on by a child widget, it necessarily sets the needsCompositing bit of its parent widget, but RenderPointerListener was ignoring that piece of information and only turning on compositing if it thought it needed it for itself.

This corrects that, and adds a test for the condition, and updates a test that was affected by the change.

Fixes flutter#32525 (again)

cherry-pick: fix edge swiping and dropping back at starting point (fl…

…utter#31623)

iOS selection handles are invisible (flutter#31332) (flutter#31862)

Fix a bug where text selection handles were invisible in iOS

Add support for the Kazakh language (flutter#31578)

[Material] Update slider and slider theme with new sizes, shapes, and…

… color mappings (2nd attempt) (flutter#31564)

flutter#30390 was rolled back. This PR will re-roll it forward.

This PR makes a number of changes to the visual appearance of material sliders:

Sizes/Shapes
** enabled thumb radius from 6 to 10
** disabled thumb radius from 4 to 10 with no gap
** default track shape is a rounded rect rather than a rect
**
Colors
** all of the colors now use the new color scheme
** overlay opacity has been reduce from 16% to 12%
** value indicator text color now respects the indicator it is on by using onPrimary
** disabledThumb color no respects the surface it is on by using onSurface
The slider theme is also now constructed consistently with other theme objects within the ThemeData. By default, all values are null, and have default values that are resolved in the slider itself, rather than in the slider theme.