Improve diagnostics and add code fixes for top-level await

[rbuckton]

This improves the diagnostic messages for top-level await and adds several code-fixes to improve the experience.

In addition, this fixes a small bug in our textChanges algorithm to ensure we correctly add new-lines when inserting nodes at the top of a class body/object literal (and elide trailing commas in an object literal when they aren't needed.

Fixes #36036
Fixes #36171

[DanielRosenwasser]

Looks like there's a merge conflict.

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@typescript-bot pack this

[typescript-bot]

Heya @DanielRosenwasser, I've started to run the tarball bundle task on this PR at 80b065f. You can monitor the build here. It should now contribute to this PR's status checks.

[DanielRosenwasser]

The message improvements look good.

I would suggest always keeping the trailing comma to be honest - but I happen to be especially prone to adding new fields after members that lack a comma.

[rbuckton]

@DanielRosenwasser: Trailing comma is illegal in JSON, so if we ever have a codefix that affects package.json, it would make that file invalid. I'd rather trim the trailing comma to be safe.

[DanielRosenwasser]

Would it be too much trouble to have the codefix check if it's in ES3 or working under JSON?

[DanielRosenwasser]

or have the printer "do the right thing" under either mode?

[rbuckton]

I've updated it so that it only elides the trailing comma when the source file is a .json file (since there's no way to tell whether it's a normal .json or a non-standard .json like our tsconfig files).