Extend screenshot timeout on accessibility events

The implementation approach comes from SystemUI's
`VolumeDialogImpl.java`.

Manual testing included both voice access and explore-by-touch a11y
modes.

Test: manual testing with extra instrumentation
Bug: 350026673
Flag: EXEMPT bugfix
Change-Id: I0f86248b8e7423cb79c5b67720e6e2b91e01f70d