Publish ContractsDsl

- Mark @ContractsDsl as @Experimental
- Move Contracts DSL out from 'internal' package
- Change visibility of ContractsDsl from 'internal' to 'public'

^KT-25274 Fixed
^KT-25495 Fixed

libraries/stdlib/src/kotlin/internal/contracts/ContractBuilder.kt

@@ -1,32 +0,0 @@
-/*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
- */
-
-package kotlin.internal.contracts
-
-import kotlin.internal.ContractsDsl
-import kotlin.internal.InlineOnly
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface ContractBuilder {
-    @ContractsDsl fun returns(): Returns
-    @ContractsDsl fun returns(value: Any?): Returns
-    @ContractsDsl fun returnsNotNull(): ReturnsNotNull
-    @ContractsDsl fun <R> callsInPlace(lambda: Function<R>, kind: InvocationKind = InvocationKind.UNKNOWN): CallsInPlace
-}
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal enum class InvocationKind {
-    @ContractsDsl AT_MOST_ONCE,
-    @ContractsDsl AT_LEAST_ONCE,
-    @ContractsDsl EXACTLY_ONCE,
-    @ContractsDsl UNKNOWN
-}
-
-@ContractsDsl
-@InlineOnly
-@SinceKotlin("1.2")
-internal inline fun contract(builder: ContractBuilder.() -> Unit) { }

libraries/stdlib/src/kotlin/internal/contracts/Effect.kt

@@ -1,36 +0,0 @@
-/*
- * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
- * that can be found in the license/LICENSE.txt file.
- */
-
-package kotlin.internal.contracts
-
-import kotlin.internal.ContractsDsl
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface Effect
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface ConditionalEffect : Effect
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface SimpleEffect {
-    @ContractsDsl
-    infix fun implies(booleanExpression: Boolean): ConditionalEffect
-}
-
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface Returns : SimpleEffect
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface ReturnsNotNull : SimpleEffect
-
-@ContractsDsl
-@SinceKotlin("1.2")
-internal interface CallsInPlace : SimpleEffect