implement posix delete on windows, if supported

[IanButterworth]

Fixes #3839

Implements posix delete for files and dirs, with fallback to the old method if not supported (e.g. Fat32)

[vtjnash]

LGTM, but will leave open for a bit in case anyone else wants to comment

[IanButterworth]

Of the two tests that are failing, I don't see a relation to this PR and:

This one is failing on the tip of v1.x #4325

not ok 32 - env_vars
# exit code -1073740791
# Output from process `env_vars`:
# Assertion failed in D:\a\libuv\libuv\test\test-env-vars.c on line 96: `r == 0` (-4071 == 0)

I take it this one might be flaky?

2: not ok 53 - fs_event_watch_dir
2: # exit code -1073740791
2: # Output from process `fs_event_watch_dir`:
2: # Assertion failed in D:\a\libuv\libuv\test\test-fs-event.c on line 201: `strncmp(filename, file_prefix, sizeof(file_prefix) - 1) == 0` (1 == 0)

[bnoordhuis]

Only a partial review due to time constraints.

[bnoordhuis]

LGTM insofar I'm able to judge that.

I note there's a TOCTOU issue in that function (checking file type before applying the operation) but that doesn't look like it's new.

[IanButterworth]

Gentle bump on this.