[clang-tools-extra] [clang-doc] add nested namespace test case (PR #97681)

[via cfe-commits]

PeterChou1 wrote:

> I think this mostly looks good, but I am concerned with the line number matching. It appears that whenever you’ve up’s the file you’ve had to update all the line numbers.
> 
> Is it feasible to rewrite some of the checks to use the “LINE” directive? Perhaps it also makes sense to move those checks close to the lines they expect to match? Another thought is to leave the test as is, but drop the line numbers(or just match any number) and have a small set of check in line with the code that checks the line numbers with the LINE directive and uses a new prefix.
> 
> https://llvm.org/docs/CommandGuide/FileCheck.html#filecheck-pseudo-numeric-variables

I don't think this possible since the line directive matches the line of the html or md file you pipe into FileCheck, which is different from the line that's define in the source code. I've opted for just matching any number to make the test case less brittle

https://github.com/llvm/llvm-project/pull/97681