Step 2 - Fix Web IDE on projects without merge requests

• Step 1 - Add read_merge_request to GraphQL ProjectPermission BE
• Step 2 - Fix Web IDE on projects without merge requests

What does this MR do?

Previously the Web IDE did not work if merge requests were disabled for a project. Because it didn't work, we also hid the Web IDE button.

This MR fixes the Web IDE so that it works in projects without merge requests and shows the "Web IDE" button if the user can still collaborate. It introduces GraphQL in the IDE codebase to detect user permissions.

Screenshots

20200212_ide_fix_no_mr_demo

Some things that have changed since this demo:

• Fixed the width of the branch section in the nav dropdown when MR's are not enabled

No MR - Disabled option + tooltip	No MR - Disabled option	No MR - branch only nav dropdown

With MR - Same ol' nav 🎉	With MR - Same ol' options

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.

References

• #35428 (closed)