[Concurrency] Add a SILGen test for isolated default arguments.

(cherry picked from commit f448684)

Author: hborla

test/Concurrency/isolated_default_argument_eval.swift

@@ -0,0 +1,25 @@
+// RUN: %target-swift-emit-silgen -I %t  -disable-availability-checking -strict-concurrency=complete -enable-experimental-feature IsolatedDefaultValues -parse-as-library %s | %FileCheck %s
+
+// REQUIRES: concurrency
+// REQUIRES: asserts
+
+@MainActor
+func requiresMainActor() -> Int { 0 }
+
+@MainActor
+func mainActorDefaultArg(value: Int = requiresMainActor()) {}
+
+// CHECK-LABEL: sil hidden [ossa] @$s30isolated_default_argument_eval15mainActorCalleryyF
+@MainActor func mainActorCaller() {
+  mainActorDefaultArg()
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s30isolated_default_argument_eval22nonisolatedAsyncCalleryyYaF
+func nonisolatedAsyncCaller() async {
+  // CHECK: hop_to_executor {{.*}} : $Optional<Builtin.Executor>
+  // CHECK: [[GETARG:%[0-9]+]] = function_ref @$s30isolated_default_argument_eval19mainActorDefaultArg5valueySi_tFfA_
+  // CHECK: hop_to_executor {{.*}} : $MainActor
+  // CHECK-NEXT: apply [[GETARG]]()
+  // CHECK-NEXT: hop_to_executor {{.*}} : $Optional<Builtin.Executor>
+  await mainActorDefaultArg()
+}