glsl: Allow less restrictive uses of sampler array indexing in GLSL <= 1.20
GLSL 1.10 and 1.20 allow any sort of sampler array indexing. Restrictions were added in GLSL 1.30. Commit f0f2ec4d added support for the 1.30 restrictions, but it broke some valid 1.10/1.20 shaders. This changes the error to a warning in GLSL 1.10, GLSL 1.20, and GLSL ES 1.00. There are some spurious whitespace changes in this commit. I changed the layout (and wording) of the error message so that all three cases would be similar. The 1.10/1.20 and 1.30 text is the same. The only difference is that one is an error, and the other is a warning. The GLSL ES 1.00 wording is similar but not quite the same. Fixes piglit test spec/glsl-1.10/compiler/constant-expressions/sampler-array-index-02.frag and bugzilla #32374.