Add strict onEnterRules for controlling indentation

[wachtel1]

Bugsquad edit: This closes #337.

[Calinou]

Just to make sure, is this good to merge now?

[wachtel1]

@Calinou Please see the behavior on the gif below.

Moving the line after the if statement down works correctly.
Pasting after the if statement works correctly.

Adding indentation by just pressing Enter works as before.
I also tested other statements that have indentation rules.

The problem I'm having with this is that I can't explain why it fixes the issue, so if someone is willing to test this config as well, as I have only one environment to test on, it would be better.

[DaelonSuzuka]

This is a big improvement over the previous behavior.

[Calinou]

Thanks!