Refactoring siVarLoc creation (dotnet/coreclr#22543)

Refactoring siVarLoc creation (dotnet/coreclr#22543)

* Moving siVarLoc and siVarLocType from compiler.h to CodeGenInterface.h

* Encapsulating siVarLoc construction with siScope and LclVarDsc

* Encapsulating siVarLoc construction from psiScope

* Adding some argument description on genSetScopInfo header

* Changing const siVarLoc& to const siVarLoc* on eeSetLVInfo

* Changing siVarLoc& to siVarLoc* in genSetScopeInfo arguments

* Rename var in genSetScopeInfo header

Commit migrated from https://github.com/dotnet/coreclr/commit/2f75b38bd75e88860203a7fad83f5fbadff0b1f4