WIP: initial GLES3.0 stuff from Pyry Haulos
Remove fixedTargetVersion
Fix some tex Lod/Grad functions lost in ES3 work
tests: towards testing GLES3 path
always emit lowp for shadow sampler precision
tests: switch to CGL from AGL on Mac; needed for 3.2 profile soon
tests: switch to core GL function names instead of ARB ones;
create two GL contexts on Mac to test;
start producing & checking GLES3 shaders (mapping to GLSL 1.50 for checks)
Fix textureCube output for GLES3+
tests: add ES3 test outputs; produces with ES2 right now
tests: update expected ES3 output
tests: no need for GLSL 1.20 array bug workaround in GLES3