Golang x/tools/gopls: support "inline all" and "inline away"

Add two new code actions for inlining, defined at the callee rather than caller:

• "inline all" inlines all uses of a function
• "inline away" inlines all uses, and additionally removes the function declaration

Comment From: adonovan

See also: - https://github.com/golang/go/issues/70085 (extract is done) - https://github.com/golang/go/issues/68567 (inline all calls within a single file)