This commit renames the original shouldPerformDiffInformedAnalysis(),
which returns `PullRequestBranches | undefined`, to
getDiffInformedAnalysisBranches(). It also adds a new
shouldPerformDiffInformedAnalysis() function that returns boolean.
Separating these two functions makes it clear what the intended uses and
return values should be for each.
Kasper Svendsen
Chuan-kai Lin