Due to recent changes a cached patch string in GLShader grew out of
its bounds. This resulted in incorrect shader generation on selected
platforms (Reported was Windows/NVIDIA). The patch string can differ
based on the features that the GPU supports.
This PR replaces the old C-style string generation with CPP-style
string stream, making sure that the allocated memory grows with the
size of the string.
Pull Request: https://projects.blender.org/blender/blender/pulls/116085
f9269312da