Closes https://tree.taiga.io/project/penpot/task/9337 and fixes https://tree.taiga.io/project/penpot/task/9421

⚠️ A screen with a device pixel ratio > 1.0 is needed to test this PR fully. You can check the pixel ratio by typing in the browser console devicePixelRatio.

In this PR:

• We take into account the device pixel ratio (aka DPR) to render shapes. This requires to have a bigger canvas to acomodate for higher pixel densities, and also bigger Skia surfaces.
• Using the DPR is walled behind a config flag enable-render-wasm-dpr.
• I introduced some refactors because the render code was a bit tricky and too long to follow.
  • The RenderState now holds the Viewbox (instead of State and passing it to RenderState in each method call)
  • Renamed Viewbox's x and y to pan_x and pan_y (since we stored them in the negative, like panning).
  • The logic to determined whether an image cached needed to be regenerated o no has been moved to its own method and now uses Skia's Rect.contains. I'm not sure if this logic mimics exactly what @superalex did (I think I need a drawing of the check he intended)

Note that a large DPR hits performance greatly (for instance 2.0 dpr for a 4K display means surfaces with 4x pixels). The avatars example file we're using gets a bit laggy when zoomed out (OTOH when we introduce more performance improvements, this will benefit as well)