Test boolean mix in glsl3

[SamueleDecarli]

GLSL ES 300 spec for boolean mix states:

genType mix (genType x, genType y, genBType a)
Selects which vector each returned component comes from. For a component of a that is false, the corresponding component of x is returned. For a component of a that is true, the corresponding component of y is returned. Components of x and y that are not selected are allowed to be invalid floating point values and will have no effect on the results. Thus, this provides different functionality than genType mix(genType x, genType y, genType(a)) where a is a Boolean vector.

This test verifies that NaN has no effect on boolean mix.

Related ANGLE bug: https://issues.angleproject.org/issues/42265719

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