For #81574

See #84669 for details of the problem around strict function types. This change converts `SyncActionDescriptor` to use a static `create` function. This allows us to make the `create` function generic so that it can take the correct types for strictFunctionTypes

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.

* Converted another ~70 test files to strictNullChecks

These are the remaining test files that didn't require any changes to non-test file types. I'll send those in separately.

Most changes were automatic and small (`!`s).
The only non-trival change is that `extHostSearch.ts` needs an interface for its test data.

Again used [TypeStat](https://github.com/JoshuaKGoldberg/TypeStat) when possible per #65581. I'm happy to split this up into smaller PRs if you'd prefer!

* Added missing `!`s to `commands.test.ts`

without instead of wihtout