vfmt: remove unused imports

[ttytm]

Resolves a TODO for vfmt adding/fixing removal of unused imports. It does so respecting user comments.

v/vlib/v/fmt/fmt.v

Lines 343 to 346 in a1b6360

	if imp.mod !in f.used_imports {
	// TODO: bring back once only unused imports are removed
	// continue
	}

I think vlib/v/fmt/tests/import_comments_expected.vv is the best file in the updated test showcasing the behavior.

Includes minor quality improvements. Next step would fixing/extending auto imports.

[spytheman]

Automatically removing unused imports is very breaking for prototyping. Imho the warning that is currently present, is more than enough.

[spytheman]

Autoimporting is imho also a bad idea, because it is a heuristic, that can not work reliably in all or even most cases, since vfmt works on single files, and thus has no idea, whether the os.abc that you wrote somewhere in a file, means that you want to import os or import myproject.os or import xyz as os.

[spytheman]

I think, we should at some point, do a cleanup of such TODO: items, that may have seemed good on the surface initially, but that turned out to have big negatives revealed later.

[ttytm]

Yes it is better to solve this via import completion of a ls. V-analyzer could support it.

[ttytm]

@spytheman should we than remove the current auto imports?