Mac: Detect new folders sooner in the vnode op event handler, remove NeedsNewFolderCreateNotification, and try enabling NeedsNewFolderCreateNotification functional tests

Possibly fixes #360 and possibly allows NeedsNewFolderCreateNotification tests to be enabled on Mac.

A few changes are needed:

1. Update ShouldHandleVnodeOpEvent to check the vnode cache rather than the FileFlags_IsInVirtualizationRoot flag when deciding if an event should be handled.

2. In the directory handling if/else code blocks here:

    if (isDirectory)
    {
        if (isRename ||
            ActionBitIsSet(
                action,
                KAUTH_VNODE_LIST_DIRECTORY |
                KAUTH_VNODE_SEARCH |
                KAUTH_VNODE_READ_SECURITY |
                KAUTH_VNODE_READ_ATTRIBUTES |
                KAUTH_VNODE_READ_EXTATTRIBUTES))
        {

https://github.com/microsoft/VFSForGit/blob/16deac4d57ab5b287de5a06ee366f1b8d4481cc2/ProjFS.Mac/PrjFSKext/KauthHandler.cpp#L533

Use if (!FileFlagsBitIsSet(currentVnodeFileFlags, FileFlags_IsInVirtualizationRoot)) to detect new folders and notify VFS4G.

3. With the above changes we should be able to remove FindNewFoldersInRootAndNotifyProvider and its associated code.

4. See if NeedsNewFolderCreateNotification can be enabled (still TBD if we're guaranteed to get a vnode op callback from simply creating a directory).

5. If with this change FileFlags_IsInVirtualizationRoot is only used to track if the provider knows about the file, rename the flag to something like FileFlags_IsTrackedByProvider