Refactor pull request view (3) (#37439)

Move some complex logic to backend

Rename `pr.CanAutoMerge` to `pr.IsStatusMergeable`

models/issues/pull.go

@@ -437,8 +437,8 @@ func (pr *PullRequest) IsChecking() bool {
 	return pr.Status == PullRequestStatusChecking
 }
 
-// CanAutoMerge returns true if this pull request can be merged automatically.
-func (pr *PullRequest) CanAutoMerge() bool {
+// IsStatusMergeable returns true if this pull request is mergeable to its base
+func (pr *PullRequest) IsStatusMergeable() bool {
 	return pr.Status == PullRequestStatusMergeable
 }