Disable autodevops by default and simplify merging

What does this MR do?

This avoids creating a pipeline that will never complete in tests that don't care about them.

This also speeds up tests and makes them less flaky. Previously, most tests involving an MR would check to see if it could be merged, or if the dropdown had to be changed to select "Merge immediately".

Finally, it reorganizes Page::MergeRequest::Show methods alphabetically because it was a pain to try to find methods and go-to-definition was being unhelpful.

Closes #36824 (closed)

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