Reset SurfaceControl when reapplying magnification spec

If there is a container becomes to non-magnifiable, we need to clear
magnification spec (reset the state) and re-traverse all children again.

Bug: 144810344
Test: A11y CTS & unit tests
Test: atest WmTests
Test: manual
      1. Enable Magnification in Settings > Accessibility.
      2. Open any app with an EditText, tap it to bring up the IME.
      3. Trigger Magnification.
      4. Check only the app should be magnified, but not IME.
      5. Switch to another IME, and check 4, again.

Change-Id: Ia04cb6c49b67dab98cee5bb0cacef12a8bdaffd8
Merged-In: Ia04cb6c49b67dab98cee5bb0cacef12a8bdaffd8