Add 'suspendWithCurrentContinuation' and 'Suspend' object in built-ins

They are part of the new suspension convention, relevant
support in backends will be added in later commits

 #KT-14924 In Progress

compiler/testData/builtin-classes/default/kotlin-coroutines.txt

@@ -0,0 +1,16 @@
+package-fragment kotlin.coroutines
+
+@kotlin.SinceKotlin(version = "1.1") public inline suspend fun </*0*/ T> suspendWithCurrentContinuation(/*0*/ body: (kotlin.coroutines.Continuation<T>) -> kotlin.Any?): T
+
+@kotlin.SinceKotlin(version = "1.1") @kotlin.annotation.Target(allowedTargets = {AnnotationTarget.CLASS}) @kotlin.annotation.Retention(value = AnnotationRetention.BINARY) public final annotation class AllowSuspendExtensions : kotlin.Annotation {
+    /*primary*/ public constructor AllowSuspendExtensions()
+}
+
+@kotlin.SinceKotlin(version = "1.1") public interface Continuation</*0*/ in P> {
+    public abstract fun resume(/*0*/ data: P): kotlin.Unit
+    public abstract fun resumeWithException(/*0*/ exception: kotlin.Throwable): kotlin.Unit
+}
+
+@kotlin.SinceKotlin(version = "1.1") public object Suspend {
+    /*primary*/ private constructor Suspend()
+}

compiler/testData/diagnostics/tests/coroutines/suspendWithCurrentContinuation.kt

@@ -0,0 +1,31 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+// !CHECK_TYPE
+class Controller {
+    suspend fun noParams(): Unit = suspendWithCurrentContinuation {
+        if (hashCode() % 2 == 0) {
+            it.resume(Unit)
+            Suspend
+        }
+        else {
+            Unit
+        }
+    }
+    suspend fun yieldString(value: String) = suspendWithCurrentContinuation<Int> {
+        it.resume(1)
+        it checkType { _<Continuation<Int>>() }
+        it.resume(<!TYPE_MISMATCH!>""<!>)
+
+        // We can return anything here, 'suspendWithCurrentContinuation' is not very type-safe
+        // Also we can call resume and then return the value too, but it's still just our problem
+        "Not-int"
+    }
+}
+
+fun builder(coroutine c: Controller.() -> Continuation<Unit>) {}
+
+fun test() {
+    builder {
+        noParams() checkType { _<Unit>() }
+        yieldString("abc") checkType { _<Int>() }
+    }
+}

compiler/testData/diagnostics/tests/coroutines/suspendWithCurrentContinuation.txt

@@ -0,0 +1,13 @@
+package
+
+public fun builder(/*0*/ coroutine c: Controller.() -> kotlin.coroutines.Continuation<kotlin.Unit>): kotlin.Unit
+public fun test(): kotlin.Unit
+
+public final class Controller {
+    public constructor Controller()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public final suspend fun noParams(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+    public final suspend fun yieldString(/*0*/ value: kotlin.String): kotlin.Int
+}