[clang] [docs] Fix the use of word "dependent" and other typos in the C++ Modules Doc (PR #136719)

[Arseniy Zaostrovnykh via cfe-commits]

necto wrote:

Hi, @ChuanqiXu9 
I've been reading through the documentation, and got confused in a couple of places. I propose these small fixes. Unfortunately, I don't know who should be assigned to review the PR, so I ping you as one of the most impactful committer to this file.

https://github.com/llvm/llvm-project/pull/136719