Enable snippets_edit_vue by default

What does this MR do?

Enables the :snippets_edit_vue feature flag by default. The main portion of the MR is related to updating the specs so that those work both in Rails application (the flag is off) and in Vue application (the flag is on).

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

References #207239 (closed)