Introduce explicit Viewport sharing

[hecrj]

This PR introduces a Viewport type that explicitly holds the Params of a Pipeline.

This allows sharing a Viewport with multiple TextRenderer instances, reducing pipeline context changes.

Depends on #95.

[grovesNL]

This looks great, thank you! Sharing Viewport explicitly seems like a good approach.

I wish we could derive this internally somehow and share params on a shared type like Pipeline. I'm not sure how we could do that without requiring something like a viewport index to be specified during screen resolution updates though.

[hecrj]

Rebased on top of main!

I wish we could derive this internally somehow and share params on a shared type like Pipeline. I'm not sure how we could do that without requiring something like a viewport index to be specified during screen resolution updates though.

Right... It doesn't seem easy to figure out which params to invalidate internally. At least, we are mostly just trading an argument here (Resolution for Viewport).