use re_renderer to draw 2d scenes

[Wumpf]

Use re_renderer instead of epaint for everything the 2d scene renders except text labels (and their boxes).

Differences are quite subtle!

before - after

after - before

after - before

(sorry for randomized order oops..)

Added transparency-enabled tinting to re_renderer to enable image layering as we had it before.

Coordinates passed to re_renderer draw data objects are all in scene coordinates! I.e. the camera/projection setup we're passing the the ViewBuilder is doing the job to go all the way from scene to pixel coordinates for us!

Direct follow-up todos:

• change the hover check to use scene coordinates (by computing the mouse position in scene coordinates). Then the only thing we need ui coordinates for is placing text labels!
• adjust data structures to not use egui color properties etc., cut out two step data conversions store->scene->renderer similar to what we did with lines in the 3d scene
• remove egui images from ImageStore? This requires rendering the hover preview also with re_renderer which is a bit excessive for the moment (but so is keeping the extra texture!)

TODO before going in:

• check more samples
• test web

(Fixes most of #382, but I'll close only after those additional items)

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I've added a line to CHANGELOG.md (if this is a big enough change to warrant it)

[emilk]

Niiice! we're getting close.

But I would feel better if #456 could be done before we merge this, so we can be sure we're not leaking GPU resources.

[emilk]

The only reason rendering and hovering was coupled together was to save on doing ui_from_space twice. Now that that has been fixed, it would be nice to separate rendering from picking completely!

[Wumpf]

agreed! Let's do so in a follow-up

addressed