Assorted cleanup of TH module

[danbroooks]

Before submitting your PR, check that you've:

• Ran stylish-haskell on any changed files.
• Adhered to the code style (see the .editorconfig file for details)

After submitting your PR:

• Update the Changelog.md file with a link to your PR
• Bumped the version number if there isn't an (unreleased) on the Changelog
• Check that CI passes (or if it fails, for reasons unrelated to your change, like CI timeouts)

---

This PR contains an assortment of various tweaks to the TH module, it inlines some functions, extracts some functions, and contains some general cleanup in the form of whitespace/alignment fixes and stylish-haskell fixes. And is also a bit of a followup on from #1218