Add sysprop for extra delay for content overlay fade out

This will only apply to gesture nav, where we set withDelay to false.

3 button nav already has a 500 ms delay built in to avoid flickers.

Bug: 291099063
Test: n/a
Flag: NONE, new integer system property with default value

Change-Id: I96db41157e1f24e00dc872e124fa24726848e638