Scroll Capture: Add configurable post-scroll capture delay

Default 60ms after next animation pulse, configurable with:

adb shell settings put global screenshot.scroll_capture_delay ##

Bug: 173700533
Test: manual - long screenshot Play Store/Google Photos
      observe that images are fully visible when captured
Change-Id: I84e0b1fd6b94d3ff7177fa00166da40b30f311cf