Add x-failed scale test for type-checking nil-coalescing dictionary values

Author: AnthonyLatsis

validation-test/Sema/type_checker_perf/slow/nil_coalescing_dictionary_values.swift.gyb

@@ -0,0 +1,10 @@
+// RUN: %scale-test --invert-result --begin 1 --end 8 --step 1 --select NumLeafScopes %s -Xfrontend=-typecheck
+// REQUIRES: asserts, no_asan
+
+let x: Int?
+
+let _ = [
+%for i in range(0, N):
+  "k" : x ?? 0,
+%end
+]