Backport 'Add ability to disable GL draws'.

This feature is intended for use in headless test environments,
where disabling drawing has minimal compatibility impact and can
save significant resource usage when running UI tests.

This feature is controlled via a new system property
'debug.hwui.drawing_enabled', and a HardwareRenderer API that can
override the property value on a per-process basis.

Bug: 201691826
Test: boot emulator
Merged-In: I93c21e680382e03342f235dbf58bd7a5c8a6f767
Change-Id: I391c841e3a0cdcfcc6c7910a316a4dd5e970547d