Allow specifying minor GLES3 version

[PJB3005]

Checklist

• Run cargo clippy.
• Run cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
Fixes #3978

Description
Adds a force_angle_gles31 flag to wgpu::InstanceDescriptor. This flag will force us to request a GLES3.1 context, which makes ANGLE provide as such on D3D11 (even though it's non-conformant).

Testing
I ran a bunch of the samples with this forced on. There were some issues I found, but I didn't diagnose them too much:

• boids doesn't seem to present correctly, but in RenderDoc it does seem to work.
• water doesn't render the water.
• sRGB when presenting is broken, so colors were messed up. Checking through renderdoc, it seems correct during internal rendering though.

[PJB3005]

Is there a better place to put it than InstanceDescriptor? The breaking change from this kinda sucks.

[cwfitzgerald]

Not really... this is where we need it. We probably should consider the ergonomics of InstanceDescriptor as this kind of thing likely will happen quite a bit.

Let's leave it as is for now.

[cwfitzgerald]

I have some concerns about how people will interpret and fill out the instance descriptor, but this is a larger question than this PR, so lets get this in.