Feature req: foldable import statements

[machty]

I noticed on .ts files that the import statements can be folded, which is a NTH when working with a file w lots of imports:

But some reason this doesn't work with .gts files; no fold arrow appears (note the missing fold arrow; the red squiggle is an unrelated thing):

This might be related to the hacks we add to the front of .gts files to get extension-less imports working correctly.