Clean Up Whitespace on Enter

[ssigwart]

Clean up whitespace when Enter key is pressed. This will:

1. Remove all whitespace lines when you hit Enter.
2. Remove whitespace from the end of something like "abc"; when you hit Enter.
3. Remove the space before the 2 if you hit Enter after the comma in 1, 2. (This also works for multi-cursor mode)

This PR fixes #61972.
It might also be a workaround for #13157 because it will remove whitespace on the lines you modify, not the whole file.

To test, you can run this:

./scripts/test.sh --glob **/cursor.test.js --grep trimTrailingWhitespace

You can also manually test by adding whitespace at the end of lines and clicking Enter.

[CelticMinstrel]

2 and 3 sound good but I don't like the sound of 1. I prefer my blank lines to match the prevailing indentation.

[ssigwart]

@CelticMinstrel, I'm not going to make any changes to this pull request until I hear from the VSCode team, but I did update my extension with an option to allow all blank lines. Since this can be accomplished with an extension and people are going to want it handled different ways, there's a chance this gets closed instead or merged.