Use .vec SVG class for vector_graphics_compiler transformed assets

[Albert221]

What does this change?

In the SVG integration, assets that have a vector_graphics_compiler asset transformer will use SvgGenImage.vec constructor to use correct bytes loader.

Fixes #684 🎯

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] This change requires a documentation update

Checklist:

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• [x] Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
  • [x] Ensure the tests (melos run test)
  • [x] Ensure the analyzer and formatter pass (melos run format to automatically apply formatting)
• [x] Appropriate docs were updated (if necessary)