chore: Remove WebGL1 support

[ibgreen]

For #

Background

• Last steering meeting indicated preliminary agreement around removing WebGL1 support.
• (deck.gl v9 won't run on WebGL1 regardless as it uses uniform buffers etc, and we want our development bandwidth focused on WebGPU, not WebGL1).
• This PR will be discussed in the Feb 1 meeting.
• The changes can land in 9.0 or 9.1, but we probably do not want to wait until v10.

Change List

• Remove WebGL1 support
• Remove GLSL 1.00 support
• Remove headless-gl support

Remaining / Follow ups

• test cleanups
• doc cleanup
• website cleanup
• Remove GLSL 3.00 -> 1.00 shader transpilation

[ibgreen]

@donmccurdy I am getting some test failures in the TextureTransform class, I can't really see what changed - and those tests were already WebGL2 only before this PR. Perhaps we can pair up early next week? It would be good to have this PR ready to merge for the Thursday open vis meeting.

[donmccurdy]

@ibgreen sorry I missed this earlier! Yes, I think I can take a look at the failing TextureTransform tests tomorrow morning.