Fix bug #7112 (Out-of-scope files added to Find in Files results)

Fix bug #7112 -- Apply all the same filtering when updating incrementally as we do when performing the initial search.  Consolidate many of these checks in a new _inSearchScope() and rename the old _inScope() to sound less confusingly similar.

Also: tweak Dialog to allow closing with Ctrl+Enter when focus is in a textarea (where regular Enter is prevented from closing). Helps filter editing.