ghc-boot-th: expose all TH packages from proper GHC.Boot.* modules

Previously we defined some modules here in the GHC.Internal namespace.
Others were merely re-exposed from GHC.Internal.

Re-exposed modules weren't handled correctly by Haddock, so the
Haddocks for the `template-haskell` library couldn't see them.
This change also makes the home package of these modules a bit clearer.

Work towards #25705