Do a little feature magic to allow to build for web

[Jengamon]

This change will allow people who want to build this crate for web (especially today) to do so, by allowing them to
transitively turn off the default wgpu features.

Turning it back on would be this crate's default feature, so current consumers wouldn't have to change anything, but
people who want web now can now do:

[dependencies]
# ... really cool deps ...
glyphon = { version = "0.5.0-whatever", default-features = false }
wgpu = { version = "0.19.1-cool-beans", default-features = false, features = ["webgl"] }

[grovesNL]

Nice, thank you!

Could we still enable the wgpu default features for the example somehow, so it does the WebGPU/WebGL fallback when building for wasm?

[grovesNL]

It looks like we still need the wgsl feature enabled unconditionally for the regular dependency