Auto Imports, remove JS/TS config

[machty]

See #130

Basic Support for Auto-Import (for all supported filetypes, including .gts)

You are now offered code completions for auto-imports, and selecting them will add the import at the top of the file.

Remove JS/TS configuration options

Previously we were attempting to read the JS/TS VScode configuration preferences in order to pass them through to the VS LSP within Glint, but since the goal is feature parity with the TS LSP such that you can (and should) disable the default TS LSP, we can't continue to use the default JS/TS config options because they get disabled then you disable the TS built-in extension. This PR replaces them with sensible hard-wired defaults, and we can consider adding configurable VS code preferences specific to Glint in a future PR.

Add localhost dev/debug instructions to CONTRIBUTING.md

This would have been very helpful for me getting up and running.

(Won't fix) Completions don't work on unclosed tags within <template>

Likely not fixable until we have some syntax-forgiving Glimmer parser.

[machty]

cc @NullVoxPopuli @dfreeman @wagenet

[machty]

Update: got auto-complete working in both .ts and .gts with default TS engine disabled.

Going to spend some time unifying the text preview to make it clearer what kind of completion/import it is.

[machty]

Pushed some updates that greatly improve the default formatting of auto imports.

[machty]

I think this PR is probably ready for a review. Here's how things ended up:

I do see one issue though:

For some reason the auto imports don't kick in depending on where you are in the tag... not sure if worth fixing in this PR or a separate issue.

[NullVoxPopuli]

Thanks a ton for adding this! This is all the information i got super stuck on not having when i was first getting in to glint!

Very needed!

[NullVoxPopuli]

Thanks a ton for adding tests!!

[spuxx-dev]

This is great! Thanks for adding this <3

[MrChocolatine]

Using these Greek letters makes the code/documentation less readable.
Why deviate from what is normally used.

[machty]

At the time of writing, these greek letters were already being used by Glint's "compiler" for transforming templates into type-checkable TS. Note that in the last year I changed these symbols to keywords like __glintDSL because I ran into upstream issues during the sourcemapping process due to the multi-byte unicode encoding for these characters.