internal/lsp: don't lower score of builtin completions
internal/lsp: don't lower score of builtin completions

Downranking builtins causes weird interplay with other completion
candidates due to fuzzy matching. For example:

notNil := 123
var foo *int = nil<>

ranks "notNil" before "nil" in the builtin list, which is counter
productive.

Change it to not downrank builtins. In my testing with this change,
builtins never were ranked above lexical items with similar names. I
think this is because the "natural" order of completion items puts
builtins last, and we stable sort items by score, so their relative
order is preserved.

Change-Id: Ifbad02be205e3cb26c1d4ce500b77690e7ac5b04
Reviewed-on: https://go-review.googlesource.com/c/tools/+/193897
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
Run-TryBot: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools