Adjust the logic of isImportantForAccessibility

According to the logic in #isImportantForAccessibility, SurfaceView
wouldn't be important by default. This results in the A11yNodeInfo
generated by this SurfaceView isn't important. If this SurfaceView
hosts an embedded hierarchy, the accessibility services may ignore
it. Hence, it couldn't compose the complete node tree.

Bug: 149266686
Test: a11y CTS & unit tests
Change-Id: I90d9f043339d2ad72607e8ae8c8dfc2c1b0f004d