Introduce inspection for redundant not-null extension receiver of inline

Related to KT-22303

core/descriptors/src/org/jetbrains/kotlin/types/KotlinType.kt

@@ -66,6 +66,8 @@ sealed class KotlinType : Annotated {
     }
 }
 
+fun KotlinType.isNullable(): Boolean = TypeUtils.isNullableType(this)
+
 abstract class WrappedType : KotlinType() {
     open fun isComputed(): Boolean = true
     protected abstract val delegate: KotlinType