Export to image with canvas (drop canvg)

[barmac]

Proposed Changes

This is a WIP branch of a migration out of canvg which fails to render some diagrams.

Known issues:

• The webhook icon diagram is exported, but the image fails to load, so it looks like this:

However, the icon loads correctly when diagram is opened. This indicates that the SVG export in bpmn-js may not work correctly.

• In the tests, we check the exact content of dataURL exported from the utility. I discovered, that in tests there are different dataURLs exported by Puppeteer's Chrome Headless 127, and my desktop Chrome 129. That may be a problem regarding the maintenance of the app since we'd need to update the snapshots, and tests would fail depending on the platform.
• Export tests in other places of the test suite started to fail with the changes even though the diagrams can be exported from the app.

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

[github-actions]

This Pull Request targets develop branch, but contains fix commits.

Consider targeting main instead.

[barmac]

Given that the main bug is in tiny-svg, I will move this PR to the backlog.

[barmac]

Export tests in other places of the test suite started to fail with the changes even though the diagrams can be exported from the app.

This is due to mock modelers exporting empty svg tag: <svg />. We should make the export realistic if this is to work.