[nodefs] Return real values for statvfs via __syscall_statfs64 #22631

[bgrgicak]

This PR was originally implemented by @jeroenpf in #22631.
I'm adding a fix for a broken test and had to do it in a new branch because I can't push to the original branch.

See #22607

statfs syscall functions are returning hardcoded default values which can in some cases lead to unexpected results.

This PR introduces a way for __syscall_statfs64 to return real values if the underlying filesystem supports this. For now, I've only implemented this for the NODEFS filesystem but we can expand this to other filesystems when it makes sense.

Additionally, in the previous defaults, ffree could be larger than files which is incorrect, this has also been addressed.

Ive added a test test/fs/test_nodefs_statfs.c which can be executed by running:
test/runner test_fs_nodefs_statfs

As I am a new contributor I'm happy to get feedback and make improvements where needed.

[bgrgicak]

I tested the failing test locally by running ./test/runner browser.test_offset_converte and it passed.
@sbc100 Am I running the correct test locally? If yes could this be a flaky test that just requires a rerun?