Bundle GitLab UI CSS with Rollup
What does this MR do and why
- Imports GitLab UI CSS files using Rollup.
- Replaces
rollup-plugin-svgwith@rollup/plugin-image. - Adjusts the nanoc build step to only copy over GitLab UI CSS source-maps.
Benefits:
- Move more frontend assets into Rollup/JS for compiling and importing.
- Fixes SVG-related issues when using GitLab UI components (this, and probably also this).
Testing
- Verify the build still works fine
- Verify GitLab UI CSS and SVGs load as expected (if GitLab UI CSS does not load, the layout will be very broken; if SVGs aren't loading, you'd see broken icons)