[pseudo] Eliminate dependencies from clang-pseudo-gen. NFC

ClangBasic dependency eliminated by replacing our usage of
tok::getPunctuatorSpelling etc with direct use of the *.def file.

Implicit dependencies on clang-tablegen-targets removed as we manage to avoid
any transitive tablegen deps.

After these changes, `ninja clean; ninja pseudo-gen` runs 169 actions only
(basically Support and Demangle).

Differential Revision: https://reviews.llvm.org/D126731