[clang-repl] [codegen] Reduce the state in TBAA. NFC for static compilation. (#98138)

In incremental compilation clang works with multiple `llvm::Module`s.
Our current approach is to create a CodeGenModule entity for every new
module request (via StartModule). However, some of the state such as the
mangle context needs to be preserved to keep the original semantics in
the ever-growing TU.

Fixes: llvm/llvm-project#95581.

cc: @jeaye
(cherry picked from commit 6c62ad446b2441b78ae524d9e700e351d5a76394)