This makes Android raw key event handling use the "character" data coming from the engine properly, and gets rid of the "toLowerCase" hack that I was using to normalize logical key events, in favor of using the new "plainCodePoint" that has the unmodified code point (the code point as if no modifier keys were pressed).
This adds support for logical and physical key information inside of RawKeyEvent. This allows developers to differentiate keys in a platform-agnostic way. They are able to tell the physical location of a key (PhysicalKeyboardKey) and a logical meaning of the key (LogicalKeyboardKey), as well as get notified of the character generated by the keypress. All of which is useful for handling keyboard shortcuts.
This PR builds on the previous PR (#27620) which generated the key code mappings and definitions.
This adds some functions to the interface for RawKeyEventData and all subclasses that allow the recipient of an event to determine which modifier keys are currently being pressed without needing to know the specific modifier bitmasks for the platform.
Also adds constants for the modifier bitmasks for each platform, for completeness (and because I needed them anyhow to implement the above).
Added tests for the RawKeyEventData subclasses, and modified the raw_keyboard manual test app to show modifier keys being pressed. I also separated the different platform-specific subclasses into separate files.
Fixes#26155.
