Replace TcLclEnv in CtLoc with a specific datatype

The TcLclEnv is used in a CtLoc for some error reporting but a large part of it isn't used.

It is problematic because it induces an import of GHC.Tc.Types from where CtLoc is defined which creates a big module cycle, because TcLclEnv contains WantedConstraints which contain Cts which contains CtLocs and so on.

From a module graph perspective this is bad, because having loops like this harms compile time.

From a logic perspective this is bad, because a CtLoc can contain a TcLclEnv which in theory could contain more CtLoc and so on. There is also no reason to presuppose that what is needed in a CtLocEnv is precisely, or a subset of a TcLclEnv. There could easily be more/different information in the CtLocEnv which is not needed by a TcLclEnv.

The solution is to define a separate type CtLocEnv which contains just what is needed for error reporting and provide a function to create a CtLocEnv from a TcLclEnv when it's needed.