A bunch of random cleanup things I found while doing MenuBar development.

Changes an if test to an assert in binding.dart, since the if should always be true.
Adds the default ShortcutRegistrar that should have been in the ShortcutRegistry PR.
Moves a debug message in the FocusManager to print the result after the focus change instead of before.
Reorders the test parameters in theme_data_test.dart to match the order of the theme data fields everywhere else.

* first pass

* x

* x

* address feedback

* support multiple extensions

* add convenience function, Object ⇒ dynamic, lerping

* remove not-useful comment

* fix examples/api lower sdk constraint

* remove trailing spaces

* remove another pesky trailing space

* improve lerp

* address feedback

* hide map implementation from constructor and copyWith

* use iterableproperty

* Revert "hide map implementation from constructor and copyWith"

This reverts commit a6994af0046e3c90dbc9405cac628feb5b2d3031.

* slow down sample

* make theme extension params required

* add null check

* improve documentation

* fix hashCode and operator == overrides

* modify existing tests

* remove trailing spaces

* add all tests except lerping

* fix lerping bug

* add toString to themeExtension example

* add lerping test

* assume non-nullability in example

* address feedback

* update docs

* remove trailing space

* use Map.unmodifiable

[Material] Use InkSparkle for splashFactory in ThemeData when useMaterial3 is true for Android non-web runtimes (#99882)

[Material] Use InkSparkle for splashFactory in ThemeData when useMaterial3 is true for Android non-web runtimes (#99882)

* Update color scheme seed generation to use color utils package

This reverts commit 78689d34.

This reverts commit 94ff5202.

This reverts commit 5fd259be.

This fixes VisualDensity.effectiveConstraints to clamp to the max values of the constraint, instead of to double.infinity.