Use glow instead of gl_generator for GL/GLES bindings

[sagudev]

See servo/servo#33539.

Note that this PR will expose glow types in surfmans public API.

[sagudev]

So the problem is that:

thread_local! {
    pub static GL_FUNCTIONS: Gl = unsafe {Gl::from_loader_function(context::get_proc_address)};
}

does not work because glow requires for context to be current, because it does some querying (version, extension). My idea is to simply replace all usages of GL_FUNCTIONS with let gl = unsafe {Gl::from_loader_function(context::get_proc_address)}; as most of the time we are already current in the calls. This would make querying every time, but functions are not hot AFAIK, so this should be ok. Alternative would be to have Gl stored on context, but this needs to be lazy value, as context creation does not make context current.

[sagudev]

I am wondering do we really need newly-created contexts that not immediately made current, or can we just made them current on creation? Linked issue on test is about something different. This was introduced in dae72e4. cc @pcwalton @jdm

[jdm]

Original issue about inconsistent behavior: pcwalton#7

[jdm]

I believe we could change the behavior to always make new contexts current.

[sagudev]

This is very close now, macos fails due to not clearing gl error before running create surface. Needs some cleanup (warnings) and updated servo companion PR.

[jdm]

If you rebase this branch on top of #326 then the crash in servo/servo#34328 will go away \o/

[mrobinson]

Is this ready to be reviewed now?

[sagudev]

Is this ready to be reviewed now?

Yes

[mrobinson]

Great stuff. I just have a few comments. In addition to what's below, please squash your changes into a single commit. Thank you!

[sagudev]

Great stuff. I just have a few comments. In addition to what's below, please squash your changes into a single commit. Thank you!

I will squash them before adding to queue.