Use `gl-hover-load` directive in Repository App for preloading Blobs when `highlight_js` disabled
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### Proposal
Currently, we use the `gl-hover-load` to preload Blobs when the `highlight_js` feature flag is enabled.
This is a proposal to implement the same enhancement when the `highlight_js` is disabled.
| type | `:highlight_js` enabled | preloads |
| ------ | ------ | ------ |
| directory | **true** | :white_check_mark: |
| blob | **true** | :white_check_mark: |
| directory | **false** | :white_check_mark: |
| blob | **false** | :x: <-- (this issue) |
issue