screenrecord: Cleanup SF APIs for creating / destroying virtual display

Follow-up CL for cleanup requested by SF owner in http://ag/27202517.
Use static const for compile-time efficiency.

Bug: 339525838
Bug: 137375833
Bug: 194863377
Test: atest libsurfaceflinger_unittest
Change-Id: Idc599f877de0c352bc759ba0b61dafc226093117