feat(elements): add Rust syntax highlighting & icon

[max-te]

As @hugo-vrijswijk suggested in #3151, this adds syntax highlighting and file icons for the Rust language. This will help integrating cargo-mutants output. The included example report.json is a result of my experimental conversion process.

[hugo-vrijswijk]

Thanks! Do you think you could replace the dark-mode file icon with a lighter colour? In light mode it looks great, but in dark mode you can't really see the icon:

Updated:

[bundlemon]

BundleMon (elements)

Files updated (3)

Status	Path	Size	Limits
✅	index.js	267.85KB (+7.38KB +2.83%)	-
✅	index.cjs	196.98KB (+5.98KB +3.13%)	-
✅	mutation-test-elements.js	196.99KB (+5.98KB +3.13%)	-

Total files change +19.35KB +3.01%

Final result: ✅

View report in BundleMon website ➡️

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Current branch size history | Target branch size history

[hugo-vrijswijk]

Thanks for this PR! I've released this in 3.1.0