Enable use of `GL_EXT_multisampled_render_to_texture` extension for OpenGL backend

[opstic]

Connections Depends on grovesNL/glow#352.

Description Enables using the GL_EXT_multisampled_render_to_texture extension when available. It enables direct multisampled rendering into a single sampled texture without needing an extra resolve operation. Saving bandwidth for mobile devices.

Testing Tested with a mobile app and looking at graphics traces/output to make sure the resolve operation is skipped and multisampling is still applied correctly.

Squash or Rebase? Squash

Checklist

• [x] Run cargo fmt.
• [x] Run taplo format.
• [x] Run cargo clippy --tests. If applicable, add:
  • [x] --target wasm32-unknown-unknown
• [x] Run cargo xtask test to run tests.
• [x] If this contains user-facing changes, add a CHANGELOG.md entry.