[mlir][Types][NFC] Move all of the builtin Type classes to BuiltinTypes.h

This is part of a larger refactoring the better congregates the builtin structures under the BuiltinDialect. This also removes the problematic "standard" naming that clashes with the "standard" dialect, which is not defined within IR/. A temporary forward is placed in StandardTypes.h to allow time for downstream users to replaced references.

Differential Revision: https://reviews.llvm.org/D92435