Minor. Use coroutine test helpers for inline/diagnostics tests

It should help with decreasing test data copy-pasting when
testing against release / pre-release coroutines

compiler/testData/codegen/boxInline/suspend/inlineSuspendOfOrdinary.kt

@@ -1,9 +1,11 @@
 // FILE: test.kt
 // COMMON_COROUTINES_TEST
 // WITH_RUNTIME
+// WITH_COROUTINES
 // NO_CHECK_LAMBDA_INLINING
 
 import COROUTINES_PACKAGE.*
+import helpers.*
 
 // Block is allowed to be called inside the body of owner inline function
 // suspend calls possible inside lambda matching to the parameter
@@ -13,17 +15,7 @@ suspend inline fun test(c: () -> Unit) {
 }
 
 fun builder(c: suspend () -> Unit) {
-    c.startCoroutine(object: Continuation<Unit> {
-        override val context: CoroutineContext
-            get() = EmptyCoroutineContext
-
-        override fun resume(value: Unit) {
-        }
-
-        override fun resumeWithException(exception: Throwable) {
-            throw exception
-        }
-    })
+    c.startCoroutine(EmptyContinuation)
 }
 
 inline fun transform(crossinline c: suspend () -> Unit) {
@@ -34,6 +26,7 @@ inline fun transform(crossinline c: suspend () -> Unit) {
 // COMMON_COROUTINES_TEST
 
 import COROUTINES_PACKAGE.*
+import helpers.*
 
 suspend fun calculate() = "OK"