Further autocomplete improvements

[dfreeman]

As with #393, this still doesn't solve our underlying "only syntactically-valid templates can produce completions" problem, but it does resolve the main issue called out in #436.

At a high level, several different related issues were coming together to produce the behavior described in #436:

• completions triggered as the result of typing a partial identifier are always considered CompletionTriggerKind.Invoked (this is per the LSP, not just a weird choice on Code's part)
• we weren't forwarding TS's sorting information through the LSP, so items didn't necessarily display in order of relevance
• standalone templates with a syntax error end up mapping to a 0-length span at the top level of the corresponding backing module, meaning that when we tried to produce completions for e.g. {{foo.}}, we'd return the full list of hundreds of available globals

Fixing those three errors, completion now looks like this:

(Note that in a loose-mode template we can't provide completions for myHashObject, as we have to assume during emit that e.g. myH is referring to some global and not an incomplete reference to a local identifier)

[chriskrycho]

This is a big improvement. Thank you, as ever.