Add Basic File Operations to the RVFileDialog

[markreidvfx]

Summarize your change.

Adds support for basic file operations within the RVFileDialog window. Please note I've not had time to test this on Windows.

Adds a context menu with the following options

• create folders
• delete files/folders
• rename files/folders
• refresh

New folder button

The New Folder button was already in the ui files. It was just hidden because it was never implemented

Describe what you have tested and on which operating system.

Linux, macOS

[pbergeron-adsk]

@markreidvfx We have found two issues with this PR:

Issue 1:

• In a folder FolderRoot that already has folders, select a folder, let's say FolderABC.
• In the empty space, right click, create new folder FolderDEF.
• User is navigated to FolderABC.

Note that if you don't select FolderABC first, the bug doesn't appear.

Expected result: User should stay in FolderRoot, optionally goes to FolderDEF, but definitely not FolderABC.

Issue 2:

• In a folder FolderRoot that already has folders, right-click in the empty space, hit Refresh, nothing happens, which is expected.

but

• Click on a folder, let's say FolderABC.
• Right-click in the empty space, hit Refresh, user is navigated to FolderABC.

They are probably different manifestations of the same bug (I'd expect that when you click on a folder, that sets the "current folder", and when you're done creating a folder, it calls refresh, which navigates to the previously-selected folder)