Test names can contain `#`. Since we ignore lines that do not match any
test names anyway, "commenting" can still work without explicit syntax.
Also drop whitespace trimming for similar reasons.
Fixes: #25741
Add `--tests-from-file <filename>` to run only the tests listed in the
given file. The test names must match exactly, no regexps or something.
The listed tests can still be filtered with a regexp using -R.
Issue: #25455