Revert to passing mIsStashed to StashedHandleViewController again

- Fixes case where handle is initially invisible but will be stashed
  and visible, e.g. when launching an app from home screen
- To fix the original issue of sampling happening unnecessarily for
  three button nav, also check supportsVisualStashing()

Fixes: 321257120
Flag: None
Test: Launch an app from home in gesture nav mode
Test: testThreeButtonsTaskbarBoundsAfterConfigChangeDuringIme
Change-Id: I1f26436de3081fd00f75a5921010e361e9a9f34e