Add a sysprop to switch between blur algorithms

Bug: 185365391
Test: adb root && adb shell 'setprop debug.renderengine.blur_algorithm kawase'   && adb shell 'stop; start' && sleep 30 && atest BlurTests
Test: adb root && adb shell 'setprop debug.renderengine.blur_algorithm gaussian' && adb shell 'stop  start' && sleep 30 && atest BlurTests
Test: adb root && adb shell 'setprop debug.renderengine.blur_algorithm ""'       && adb shell 'stop; start' && sleep 30 && atest BlurTests
Merged-In: Ib977e1d54eb08946449d447101a0c65273aa3b40
Change-Id: Ib977e1d54eb08946449d447101a0c65273aa3b40