Was multiplying matrices backward, so concatenation was broken. Fixed!
Also a way to mix legacy matrix stacks with the new library. Just during the transition! Anything within SUPPORT_LEGACY_MATRIX will go away after we switch to core profile.
Part of T49450
Built-in shaders now use uniforms instead of legacy built-in matrices. So far I only hooked this up for new immediate mode.
We use the same matrix naming convention as OpenGL, but without the gl_ prefix, e.g. gl_ModelView becomes ModelView.
Right now it can skip the new matrix stack and use the legacy built-in matrices app-side. This will help us transition gradually from glMatrix functions to gpuMatrix functions.
Still some work to do in gpuBindMatrices. See TODO comments in gpu_matrix.c for specifics.
Complete (for our needs) 2D & 3D transformation API. Should be easy to port legacy OpenGL matrix stack-based code to this. Still needs testing.
Ported ortho, frustum, lookAt functions from Viewport FX (rB194998766c65). Kept plenty of Viewport FX code from previous commit.
Stack API and 2D routines ported from Gawain. This version uses BLI_math library so everything is licensed under GPL instead of the usual MPL.
Part of T49450
