Import suggestions for out of scope type class methods in instance declarations

[Jashweii]

Example:

data X = X
instance Semigroup X where
  (<>) _ _ = X
  -- stimes is not imported
  stimes _ _ = X

HLS should suggest importing stimes (it does if instead used in an expression), and should probably import when using the "add placeholders for ". (Note it could be a qualified import.)

(GHC 8.10.4, cabal 3.2.0.0, stack 2.5.1 (unused), hls 0.9.0.0 (built from latest source), vscode)

[July541]

Close and continue in a smaller scope. #3017