posix: fnmatch: fix known bugs

[cfriedt]

Describe the bug
It appears as though the original fnmatch() implementation that was checked-in with 486b731 has bugs. This is not surprising since it was checked-in without any test coverage.

The actual failing cases are commented-out in tests/lib/posix/common/src/fnmatch.c (part of #55184)

Please also mention any information which could help others to understand
the problem you're facing:

• What target platform are you using? N/A
• What have you tried to diagnose or workaround this issue? Comment-out known failure modes in the test
• Is this a regression? No, the bugs have always been present

To Reproduce
Steps to reproduce the behavior:

1. Uncomment failure modes in tests/lib/posix/common/src/fnmatch.c
   2.west build -p auto -b qemu_cortex_a53 -t run tests/posix/common/
2. See error

Expected behavior
All test cases should pass, including known failure modes.

Impact
The shell has been using a buggy version of fnmatch() since approximately 2018.

Logs and console output

*** Booting Zephyr OS build zephyr-v3.3.0-475-gec19849fec26 ***
Running TESTSUITE posix_apis
===================================================================
START - fnmatch

    Assertion failed at WEST_TOPDIR/zephyr/tests/posix/common/src/fnmatch.c:35: posix_apis_fnmatch: fnmatch("[[?*\\]", "\\", 0) is non-zero

 FAIL - fnmatch in 0.001 seconds
===================================================================

Environment (please complete the following information):

• OS: Any
• Toolchain (e.g Zephyr SDK, ...): Zephyr SDK v0.15.2
• Commit SHA or Version used: b83cf1f but goes as far back as 486b731

Additional context
Noticed in the context of #55185

[cfriedt]

Changed to priority low, as these are not new bugs by any means, just newly discovered, and so any code that exists already in main is should continue to be stable even without an immediate fix.

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