[llvm] [llvm-lit][test] Precommit tests for lit's built-in cat command (PR #101530)

[via llvm-commits]

connieyzhu wrote:

I realized I somehow grepped incorrectly, and there actually already exists tests for `cat`. In my most recent patch, I've removed the test files I made and added a new test for `-e` in the existing file. Sorry for the inconvenience, I appreciate your patience.

> As above, consider adding `--implicit-check-not={{.}}`, `--strict-whitespace`, and `--match-full-lines` to the FileCheck commands.

@jh7370 I've added these options to the new `-e` test I added to `valid-shell.txt`. The other existing tests in this file don't seem to have these options set for FileCheck, and also have grammar/punctuation issues that you mentioned before. Do you think I make these changes to the existing tests too?

https://github.com/llvm/llvm-project/pull/101530