[clang] [Modules] No transitive source location change (PR #86912)

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

Rebase with main and enabling the sequence optimization when the module file index is 0. Now the size of the PCMs goes to 204M (originally it is 200M). It looks better.

@jansvoboda11 @Bigcheese ping

https://github.com/llvm/llvm-project/pull/86912