Pull request conflict files detection (#5951)

* add conflict detection

* test pull request conflict files

* fix detection files number

* fix comments

routers/repo/pull.go

@@ -345,6 +345,11 @@ func PrepareViewPullInfo(ctx *context.Context, issue *models.Issue) *git.PullReq
 		ctx.Data["WorkInProgressPrefix"] = pull.GetWorkInProgressPrefix()
 	}
 
+	if pull.IsFilesConflicted() {
+		ctx.Data["IsPullFilesConflicted"] = true
+		ctx.Data["ConflictedFiles"] = pull.ConflictedFiles
+	}
+
 	ctx.Data["NumCommits"] = prInfo.Commits.Len()
 	ctx.Data["NumFiles"] = prInfo.NumFiles
 	return prInfo