Always consider the "passthrough" commmand enabled for keybindings

[tsmaeder]

What it does

Theia has a "passthrough" command that is supposed to mark occasions where keystrokes are supposed to be passed to the target widget instead of being handled by the keybinding infrastructure. We recently added a check whether a keybinding has an enabled command handler to be considered active. But since the "passthrough" command has no handler, it was always considered disabled. This PR considers the passthrough command as always enabled.

Fixes #13560

Contributed on behalf of STMicroelectronics

How to test

Make sure ctrl-c aborts running tasks in the terminal. Make sure ctrl-c still works to copy text/files, etc elsewhere.

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[tsmaeder]

@jonah-iden could you make sure your recent notebook command fixes are not broken by this one?

[jonah-iden]

sure I'll take a look later today

[jfaltermeier]

LGTM. Operations in the terminal are cancellable again and other copy+paste operations don't seem to be affected.
From my pov we can merge this when the notebook commands work as well.

[jonah-iden]

@tsmaeder seems like everything still works correctly for the notrebooks