Fixing PBR on <= GLSL 130:

[MeFisto94]

• GLSLCompat now implements mat3(mat4) and determinant() and inverse() for mat2 and mat3
• PBR.glslib uses this functions again instead of one-off workarounds

[pspeed42]

Code looks good to me.

[MeFisto94]

https://github.com/MeFisto94/test-spotbugs/runs/560300340#step:5:1972 which refers to https://github.com/MeFisto94/test-spotbugs/runs/560300340#step:5:1280
Any idea? To me it reads like it didn't expect the function name, as in I cannot use mat3 as function return type? (Notice the column 6), but maybe it's some basic GLSL Syntax fault?

Edit: Confirmed with an online glsl editor: mat3 cannot be used as a function name (reserved keyword).

Follow up commit underway.

[MeFisto94]

Green lights, https://github.com/MeFisto94/test-spotbugs/runs/560327969?check_suite_focus=true#step:5:1174, going to merge

[stephengold]

Included in v3.3 branch at f68d889.