Calculate filename hash only once (#19654)

* Calculate hash only once.

* remove unused Sha1 template helper function, use ctx.Data["FileNameHash"]

* fix unit tests

routers/web/repo/compare.go

@@ -874,7 +874,7 @@ func ExcerptBlob(ctx *context.Context) {
 		}
 	}
 	ctx.Data["section"] = section
-	ctx.Data["fileName"] = filePath
+	ctx.Data["FileNameHash"] = base.EncodeSha1(filePath)
 	ctx.Data["AfterCommitID"] = commitID
 	ctx.Data["Anchor"] = anchor
 	ctx.HTML(http.StatusOK, tplBlobExcerpt)