Add TurbulenceNoiseShader.SIMPLEX_NOISE_SIMPLE.

This simplifies the usage of TurbulenceNoiseShader for users who are only interested in mixing between two colors and don't want to deal with luma matting.

Bug: 369209144
Fix: 369209144
Test: atest TurbulenceNoiseShaderTest
Flag: EXEMPT not integrated anywhere yet.
Change-Id: I70cd137fc38300dc9582e3af32ce5a9adf609269