Fix Template Haskell bug reported in #11809.

Record selectors of data types spliced in with Template Haskell are not
renamer-resolved correctly in GHC HEAD. The culprit is
`newRecordSelector` which violates notes `Note [Binders in Template
Haskell] in Convert.hs` and `Note [Looking up Exact RdrNames] in
RnEnv.hs`. This commit fixes `newRecordSelector` accordingly.

Test Plan: ./validate

Reviewers: thomie, mpickering, bgamari, austin, simonpj, goldfire

Reviewed By: goldfire

Differential Revision: https://phabricator.haskell.org/D2091

GHC Trac Issues: #11809