Reduce file system calls during test setup.

[dragomirtitian]

Improvements to reduce fs calls during test discovery:

1. Use opendirSync to read the directory content. This reduces the need to call fs.existsSync and fs.statSync
2. Cache enumerateTestFiles result to avoid having to enumerating the files again
3. Delay creation of vfs for project tests (as creating the vfs also mounts real folders which also touch the file system)

Improvements in test discovery time (anecdotal):

1. Linux node 18 debug - ~1.4 seconds -> ~800ms
2. Windows 10 node 20 debug - 8s -> 2s

Performance of running all the tests does not appear to be impacted as the cost of test discovery is not a big percentage of running all tests and the work that si delayed will have to eventually be executed anyway.

Fixes #56790

[jakebailey]

Looks good, though there's still an open thread about another function that could use withFileTypes.

That being said, I also don't see as great of an improvement as your benchmark; before:

Benchmark 1: hereby runtests -t "notarealtest" --no-typecheck --no-lint
  Time (mean ± σ):      2.265 s ±  0.012 s    [User: 2.540 s, System: 0.652 s]
  Range (min … max):    2.250 s …  2.286 s    10 runs

After:

Benchmark 1: hereby runtests -t "notarealtest" --no-typecheck --no-lint
  Time (mean ± σ):      2.093 s ±  0.039 s    [User: 2.351 s, System: 0.559 s]
  Range (min … max):    2.035 s …  2.155 s    10 runs

8% faster is still good, but you had seen 75% faster...

[sheetalkamat]

This looks ok to me except @jakebailey s suggestion on just replacing listFiles and getAccessibleFileSystemEntries to use ts.sys.getAccessibleFileSystemEntries

[dragomirtitian]

This looks ok to me except @jakebailey s suggestion on just replacing listFiles and getAccessibleFileSystemEntries to use ts.sys.getAccessibleFileSystemEntries

@sheetalkamat One small problem is that getAccessibleFileSystemEntries is not exposed in sys. I exposed it as internal. hope that is ok. I rewrote listFiles to use the sys version and also removed the local implementation of getAccessibleFileSystemEntries

[jakebailey]

I don't think that it matters, but every other function in this list is an arrow function into sys, not the actual value.