Remove indirections for WebGL texture parameters

[nox]

All parameters handled in gl.getTexParameter don't need to go through IPC.

[anholt]

getTexParameter shouldn't be a performance path, as applications are expected to never call get*

[nox]

While this is true, it also means that the associated tests run quite slowly, and all the IPC code to do those glGet calls need to be maintained. Implementing those calls purely on the DOM side still seems beneficial to me.