Clean up synonyms, key code generation.

[gspencergoog]

Description

This cleans up how synonyms are calculated, and adds a reverse mapping from pseudo keys to the real keys they are synonyms of.

Updates the layout_goals.json to include the "Space" key, since that was added in the engine without updating the generation configuration.

[dkwingsmt]

How do you plan to use this expandSynonyms? I don't see it referred in this PR.

[gspencergoog]

do you plan to use this expandSynonyms? I don't see it referred in this PR.

That's because I split this out from the shortcuts PR.

See here: https://github.com/gspencergoog/flutter/blob/activator_accepts/packages/flutter/lib/src/widgets/shortcuts.dart

(Specifically here and here)

[dkwingsmt]

I think this logic is so simple that it should probably be written as a switch clause whose default is assert(false).

[gspencergoog]

I'm not quite sure what you mean: do you mean removing the _reverseSynonyms map and just hard coding it here? Or do you mean something else?

For example:

  return input.expand((LogicalKeyboardKey key) {
    return switch(key) {
      LogicalKeyboardKey.shift => <LogicalKeyboardKey>[LogicalKeyboardKey.shiftLeft, LogicalKeyboardKey.shiftRight],
      // ...
      _ => <LogicalKeyboardKey>[key],
    };
  });

[dkwingsmt]

Yeah. I think saving a map is clearer. But it's up to you.

Also, do we expect this function to be used by others, or is it just for internal variables like _controlSynonyms? If the latter, then we might as well just use _ => assert(false) instead of _ => <LogicalKeyboardKey>[key].

[gspencergoog]

I was writing it expecting it to be generally useful. If it was just for internal variables, I'd just hard code those as private lists. I wanted to have the internal variables depend on the generated file, though, so that it wouldn't need to be updated manually if the list of synonyms gets added to. And if I wanted that, then anyone else needing this functionality might also want to do that.

[dkwingsmt]

Got it, ok, let's keep the current approach.

[dkwingsmt]

LGTM