[Add Library Dialog] [Accessibility] Hard to select individual library files using keyboard (bad tab order)

[alexgav]

Functional impact

If you use keyboard with Add Library Dialog UI, it's hard to select individual files. You need to tab to destination, then Shift-Tab from there to get to file list tree

Minimal repro steps

1. Invoke Add Client Library dialog
2. Type in some library with multiple files, e.g. jquery
   transport=longPolling)
3. Try getting to file selection tree to select individual files using keyboard

Expected result

• I would expect that from the Choose specific files radio button you'd tab to the file selection tree*

Actual result

• Tabbing from Choose specific files radio button takes you to the Target Location instead. Shift+Tab from Target Location takes you to the file list. Not sure why normal tabbing order skips the file list*

Further technical details

Seems that we need to fix focus/tab order here