add lazy loading for LocalFileResult
add lazy loading for LocalFileResult

Summary:
Since these objects result in immediate stat() calls to
fill in missing information, we don't have a nice way to batch
these up, so we just defer the stat calls until needed.

Reviewed By: strager

Differential Revision: D8584084

fbshipit-source-id: b85d866f4adcedd1a46dc18165a144e07aad719f

wez/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,wez/watchman,facebook/watchman,facebook/watchman,wez/watchman,facebook/watchman,nodakai/watchman,wez/watchman,wez/watchman,wez/watchman,wez/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,facebook/watchman,nodakai/watchman,nodakai/watchman,nodakai/watchman,wez/watchman,nodakai/watchman