Step 2 - Use arraybuffer for binary files in Web IDE

• POC
• Step 1 - Update IDE to track mimeType
• Step 2 - Use arraybuffer for binary files in Web IDE
• Step 3 - Use ide.files.change for live preview
• Step 4 - Use gitlab-smooshpack behind feature flag

What does this MR do?

In the upcoming Live Preview enhancement we will handle fetch requests in the Live Preview environment from the IDE itself.

It looks like when axios turns binary content into a String, it does so in a lossy way. To make sure we have the right content to send back to the Live Preview service worker, we need to tell axios to handle these as an arraybuffer.

Screenshots (strongly suggested)

Opening binary files still works

Does this MR meet the acceptance criteria?

Conformity

• [ ] Changelog entry Not needed because there's no user-facing change.
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