mesa: default FixedSampleLocations to true when using a dummy image
mesa: default FixedSampleLocations to true when using a dummy image

GL_ARB_texture_multisample and GLES 3.1 expect the initial value to be
GL_TRUE. This fixes

dEQP-GLES31.functional.state_query.texture_level.texture_2d_multisample_array.fixed_sample_locations_integer

and a few related tests.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Chris Forbes <5dcac483e7a6e31a5cbe89f38cc69dff8ee93dac@ijw.co.nz>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler