[lint] make grep_linter.py portable
grep_linter.py was using the `-P` flag of `grep`, which is available in
GNU grep but notably *not* available in the BSD grep that is installed
on Macs.
Use `-E` instead, which uses ERE instead of PCRE. Sadly we were actually
using two PCRE features in our linters:
- Negative lookaheads. I changed these to less-accurate-but-still-good-enough
versions that use `[^...]` expressions.
- Apparently ERE doesn't support the `\t` atom lol. So I used a literal tab
character instead (and then had to disable the TAB linter for
`.lintrunner.toml` lol.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76947
Approved by: https://github.com/ezyang
