SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Continues the migration of our code over to the fmt logger.

The strings end up being copied, so we might as well initialize the
std::string in the unordered_map directly.

Can be used for asynchronous readback or upload of textures.

The spec says it should have an EXT not OES suffix, as it's enabled as
an interaction with GL_EXT_multi_draw_arrays.

On some drivers GetProcAddress() returns NULL, which causes the
GLExtensions init to fail

This 'happened' to work if GetProcAddress() doesn't return NULL on missing
functions (as allowed in EGL) - as the function appears to never be called so
this would not have been noticed.

Mesa also (incorrectly?) exports the EXT version, so this would all
happen to work there, but appears to be contrary to the spec.

This invalid prefix even ended up in the upstream khronos registry, the
issue was reported here:
https://github.com/KhronosGroup/OpenGL-Registry/issues/81