Unwrapped ide/index.js from DOMContentLoaded handler

What does this MR do?

Moves the Vue app bootstrapping out of the DOMContentLoaded handler. See #262402 (closed) for the reference.

Screenshots

No visual changes

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #262402 (closed)