Tactics: suggest monomorphic functions that are "barely not imported"

[ProofOfKeags]

One of the nice things about HLS today is that it removes almost all of the cognitive load from having entirely specified import lists. Having every import specified in the parens helps readers of the code who may wish to do source diving but can't figure out where a definition came from. This, however, comes at a cost: the tactics engine doesn't suggest functions that are not imported. Given something like this:

import Data.Text.Encoding (decodeUtf8)

to suggest encodeUtf8 if it needs to satisfy an expression Text -> ByteString