[request] Orthographic projection and axis-aligned views in the 3D Viewer

Is your feature request related to a problem? Please describe.

The 3D Viewer only offers a perspective camera (projectionType is hardcoded to CameraLens.PerspectiveProjection). Foreshortening makes it hard to judge directions and proportions: something that looks vertical on screen can be several degrees off, and there is no way to look along a principal axis. Checking by eye whether a reconstructed facade was perpendicular to a computed projection axis left me with a 25 degree error.

Describe the solution you'd like

A toggle between perspective and orthographic projection, plus Top / Front / Side and Flip buttons, next to the existing render mode buttons.

Describe alternatives you have considered

Rotating the scene by hand and comparing it against the reference grid (imprecise, for the reason above), or exporting the geometry to another 3D application just to look at it orthographically.

Additional context

Orthographic mode was mentioned in passing at the end of #616 (2020) but never implemented. I have a working implementation and will open a draft PR.