Simplify key handlings in code hint manager.

[RaymondLim]

Set lastChar for "enter" and "tab" keys regardless of whether we're in a hinting session or not. This fixes issue #2691.

Remove code that dismisses code hints on pressing some keys with modifier keys. So we no longer dismiss code hints when a shortcut is pressed. We will have to fix the issue of code hints dismissal with another solution, but definitely not with key handling. This change fixes issue #2539.

[redmunds]

The fix for #2691 looks good. One related case I notice is that the hint list does not reposition after undo/redo. Let me know if you want to try to fix it in this pull request, or maybe just add it to that issue and keep it open for now.

[redmunds]

Undo is also causing a problem with the fix for #2539 using this recipe:

1. In a valid rule, type "b"
2. CSS hints are displayed and filtered for "b"
3. Undo

Results:
The hints list is still displayed (which is expected), but it's still filtered for "b"

Expected:
The hints list shows entire list of properties with no filtering

I am also seeing this in master, but I am surprised that the hints list is not dismissed when I perform Undo using main menu (as opposed to Ctrl-Z). Is this a bug?

[redmunds]

Done with initial review.

[RaymondLim]

Yes, we need to fix undo/redo not updating and repositioning the hint list in this pull request. We need to bring back the original key handling by simplifying more in our current key up handling.

[RaymondLim]

Ready for re-review.

[redmunds]

Looks good. Merging.