Introduce UnsafeVariance annotation

compiler/testData/diagnostics/tests/generics/suppressVarianceConflict.kt

@@ -0,0 +1,17 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_VARIABLE
+
+class A<out T, in E> {
+    fun foo(x: @UnsafeVariance T) {}
+    fun foo(x: @UnsafeVariance T, y: List<@UnsafeVariance T>): @UnsafeVariance E = null!!
+
+    fun bar(): List<@UnsafeVariance E> = null!!
+}
+
+fun foo(x: A<String, Any?>, cs: CharSequence, ls: List<CharSequence>) {
+    val y: A<CharSequence, String> = x
+
+    y.foo(cs)
+    val s: String = y.foo(cs, ls)
+
+    val ls2: List<String> = y.bar()
+}

compiler/testData/diagnostics/tests/generics/suppressVarianceConflict.txt

@@ -0,0 +1,13 @@
+package
+
+public fun foo(/*0*/ x: A<kotlin.String, kotlin.Any?>, /*1*/ cs: kotlin.CharSequence, /*2*/ ls: kotlin.List<kotlin.CharSequence>): kotlin.Unit
+
+public final class A</*0*/ out T, /*1*/ in E> {
+    public constructor A</*0*/ out T, /*1*/ in E>()
+    public final fun bar(): kotlin.List<@kotlin.UnsafeVariance() E>
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public final fun foo(/*0*/ x: @kotlin.UnsafeVariance() T): kotlin.Unit
+    public final fun foo(/*0*/ x: @kotlin.UnsafeVariance() T, /*1*/ y: kotlin.List<@kotlin.UnsafeVariance() T>): @kotlin.UnsafeVariance() E
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}