[BROWSEUI][SHELLFIND] Change the focus to the default input field

0.4.14-dev-39-gcd2a274 gcc dbg lin.

When opening our search feature via Startmenu->Search or via Winkey+F
there is no keyboard input focus on any of the edits, which means one can not simply start to type after opening the dlg.

I recommend we set the default keyboard input focus to the "filename" edit
to improve user XP.