Consume icon.json files as assets

What does this MR do and why?

Consume icon.json files as assets

Instead of loading icons.json and file_icons/file_icons.json from node_modules/@gitlab/svgs/dist, we can also make them assets and consume them from the asset pipeline. This means that if assets are pre-compiled inside of compile-test-assets, they will be included in the asset bundle and our rspec tests can pass without relying on the node_modules folder.

Contributes to gitlab-org/quality/engineering-productivity/master-broken-incidents#5793 (closed).

MR acceptance checklist

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Screenshots or screen recordings

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How to set up and validate locally

• bin/spring rspec spec/helpers/icons_helper_spec.rb