x/tools/gopls: take address automatically for completion candidates

[muirdm]

In cases like:

type B interface {
	Banana()
}

type impl struct{}

func (*impl) Banana() {}

func _() {
	var b B
	var myImpl impl
	b = <>
}

You don't get the desired candidate "&myImpl" because we don't automatically take a reference for completion candidates. I propose we count "myImpl" as a matching candidate and automatically include an additional edit to prepend the "&" reference operator. That way you can start typing "my<>" and complete straight to "&myImpl".

[gopherbot]

Change https://golang.org/cl/212399 mentions this issue: internal/lsp: support taking address for completion candidates