gh-117431: Adapt bytes and bytearray .startswith() and .endswith() to Argument Clinic

[erlend-aasland]

This change gives a significant speedup, as the METH_FASTCALL calling convention is now used.

• Issue: Improve performance of startswith, endswith, count, *find, and *index methods for str, bytes and bytearray #117431

[erlend-aasland]

Release build on macOS:

# main
$ ./python.exe -m timeit -s "b = b'abcdef'""b.startswith(b'abc')"5000000 loops, best of 5: 89.6 nsec per loop
# this PR
$ ./python.exe -m timeit -s "b = b'abcdef'""b.startswith(b'abc')"10000000 loops, best of 5: 27.3 nsec per loop

[bedevere-app]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[erlend-aasland]

Thanks for the review, Inada-san!