Customize lock screen button dismissed too fast for a11y users

We should still let the accessibility manager decide how long the
timeout should be. To better reflect the type of popup this is, add
`AccessibilityManager.FLAG_CONTENT_CONTROLS` to the `uiContentFlags`.

This will increase the timeout for this button from 5s to ~10s.

Fixes: 318029165
Test: manual testing, enable talkback, activate long-press, observe longer timeout
Flag: NONE a11y fix
Change-Id: I6512af27fa9c5833fabf8e0dfcdc7262970a60be