- Change the names of the fields in in `data FieldOcc`
- Renames `HsRecFld` to `HsRecSel`
- Replace `AmbiguousFieldOcc p` in `HsRecSel` with `FieldOcc p`
- Contains a haddock submodule update

The primary motivation of this change is to remove
`AmbiguousFieldOcc`. This is one of a suite of changes improving how
record syntax (most notably record update syntax) is represented in
the AST.