Extract PmTypes module from PmExpr and PmOracle

Apparently ghc-lib-parser's API blew up because the newly induced cyclic dependency between TcRnTypes and PmOracle pulled in the other half of GHC into the relevant strongly-connected component.

This patch arranges it so that PmTypes exposes mostly data type definitions and type class instances to be used within PmOracle, without importing the any of the possibly offending modules DsMonad, TcSimplify and FamInst.