KeyboardListener keysPressed doesn't work with Properties from HotkeyData

[jessegreenberg]

Original comment from @samreid in phetsims/number-pairs#324 (comment).

Using keyStringProperties with KeyboardListener does not work fully because keysPressed still provides hard-coded key strings even if the mapped keys are changed for i18n or remapping. This means listeners cannot know the actual remapped key values. Scenery should provide a way to access the resolved Property-driven key values in the callback, such as via pressedKeyStringPropertiesProperty or an equivalent API.

[brent-phet]

Per @jessegreenberg this would allow support for i18n key mapping.
Per @terracoda could conflict with browser key settings if keys are changed in sims.
Per @kathy-phet needs research. What is the "norm"?

[jessegreenberg]

Removing my assignment since this is not a priority right now.