This attempts to reland #40186 and #41220, that were reverted in #41945.
The main modifications from the original PRs are that I predefine the shortcuts and actions maps instead of defining them inline in the build function, and I use a new mapEquals to do a deep comparison so that we don't rebuild modified things if the contents of the map haven't changed.
I also eliminated an operator== and hashCode that were defined on the Actions widget, since widgets shouldn't have those. (it's too bad though: I get an 85% speedup if we leave this in! Too bad it prevents rebuilding of the children...)
Fixes#40101
For G3 Roll:
* Revert "MaterialButton must honor its minWidth and height parameters (#22919)"
This reverts commit a02332335a.
* Revert "Update uses of ButtonTheme.bar: pass along the current Theme's colorScheme (#22827)"
This reverts commit 655bf6a290.
* Revert "ButtonTheme.of().colorScheme defers to Theme (#22880)"
This reverts commit a590940e45.
* Revert "Bring TextTheme into alignment with the current Material spec (#22330)"
This reverts commit 8bfb4b3ee5.
* Revert "Added ColorScheme, updated ThemeData, ButtonTheme, material buttons (#22013)"
This reverts commit eea3465ae7.
* Manual adjustments to fix reversion issues.
Introduce an overall material "color scheme" and to make it possible to redefine how a component's visual properties bind to the color scheme and to the existing material Theme.
* Make CupertinoApp and MaterialApp both use WidgetsApp for Navigator
* Make CupertinoApp and MaterialApp const constructors
* Make WidgetsApp routes aware
* Update tests
