fix: add GitUtils.findBranchesNoMergeInfo and use it when merge info …

[ziggystar]

Creates a new method JGitUtil.getBranchesNoMergeInfo that does not perform the expensive repo walks. Then use this method in API requests to list branches.

This is a partial fix for #3434 which improves performance for the API requests. Rendering of the branches page of the repo is still slow.

Maybe renaming the existing method getBranches to getBranchesWithMergeInfo instead would be a better approach, since the new method should be used whenever possible.

[ziggystar]

I've added a test case that compares the output to the existing findBranches.

There's also a second commit, where I added some override annotations and a return type. I needed the overrides in my IDE for compilation. Don't know whether you want that commit, too.

[takezoe]

Thank you! Looks very good to me!!