pdInput: separate key tracker routines to prepare for new key bundles
pdInput: add Edit key bundle tracking

Edit keys are Return, Enter, Insert, Delete, Backspace, Space, and Tab.
These keys can now be separately tracked via the _KeyDownEdits() event.

Many other pdInput updates in this commit, including:
- More improvements to generalizing key tracking
- Do not raise a key bundle event if no keys relevant to that bundle
have been pressed
- Add Shift modifiers to all key events
- Change key tracking subs to functions, and return TRUE if an event was
raised (less code than the old isRelevantKeyAffected() function)
Layer toolbox: replace old key hook code with new pdInput features

New pdInput features make it *much* less work to support the
"double-click to edit layer name" feature.