Do not override insets frame if not set

Only set imeFrameProvider if the value is set in the base layout params.
This will improve the performance as the null provider can be skipped,
in the meanwhile, it will fix an error where the ime frame is
accidentally overridden.

Test: KeyboardVisibilityControlTest (CTS, on auto builds)
Bug: 229346670
Change-Id: Iaf6298e81c92b8dd221cae79e6391799b8023e95