SF: pass Color as float to HWC

In HWC3 Color is represented as a float [0.0 - 1.0] to be consistent
across the stack. SF passes the color as float and it gets translated
back to uint8_t for HWC2.

Bug: 207139550
Test: atest SurfaceFlinger_test
Change-Id: I83867eed70bd3baa3292c9cc099d891ba9cc6183