op: Implement 'simple_blend_color,blend_constant_non_inherited' test in blending.spec.ts (#1987)
op: Implement 'simple_blend_color,blend_constant_non_inherited' test in blending.spec.ts (#1987)

This PR implements a new test to ensure the blending constant is not inherited
between render passes.

Issue: #1835
gpuweb/cts,gpuweb/cts,gpuweb/cts