The major change with the unit tests was no longer requiring
a secondary null field for dispatchparts. As chords can be any length,
it's more forward-thinking to modify the unit tests to accept new behavior.

As a start to support key chords of longer than two parts,
modifying the internal structure of ChordKeybinding to not specifically
call out two parts.

* Manually added strict null checks in around 70 files

* Fixed tsconfig.strictNullChecks.json merge fail

* Touched up a few unnecessary type changes

* Removed files already in other PRs

We set alwaysStrict so this directive is not needed

Standardizing syntax and discouraging use of `this` inside tests