tac: add regex flavor translation for compatibility and new test case

[FidelSch]

Adresses #10320

Added a function to make any necessary translations to input regex in order to make them regex compatible.
Done to translate \| into | for now, but should be easy to add any other cases that come up in the future.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tty/tty-eof (fails in this run but passes in the 'main' branch)

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.

[sylvestre]

Suggested change

	.stdout_contains("cba");
	.stdout_is("cba");

[sylvestre]

you only handles \| but BRE has other differences (\(, \), \{, \} for grouping/repetition).
maybe do that now (and add tests)

also unnecessary explicit type annotation

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/seq/seq-epipe is now passing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)