Clarify path param naming (#32969)

In history (from some legacy frameworks), both `:name` and `name` are
supported as path path name, `:name` is an alias to `name`.

To make code consistent, now we should only use `name` but not `:name`.

Also added panic check in related functions to make sure the name won't
be abused in case some downstreams still use them.

services/repository/files/file_test.go

@@ -99,7 +99,7 @@ func getExpectedFileResponse() *api.FileResponse {
 func TestGetFileResponseFromCommit(t *testing.T) {
 	unittest.PrepareTestEnv(t)
 	ctx, _ := contexttest.MockContext(t, "user2/repo1")
-	ctx.SetPathParam(":id", "1")
+	ctx.SetPathParam("id", "1")
 	contexttest.LoadRepo(t, ctx, 1)
 	contexttest.LoadRepoCommit(t, ctx)
 	contexttest.LoadUser(t, ctx, 2)