Optimize memory footprint for case of empty annotations in types

It seems that most of the simple types don't have any annotations,
so for that case it's worth removing the field from SimpleTypeImpl

Also introduce a NotNullSimpleType being used when replacing nullability

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

@@ -45,7 +45,7 @@ object KotlinTypeFactory {
             return constructor.declarationDescriptor!!.defaultType
         }
 
-        return SimpleTypeImpl(annotations, constructor, arguments, nullable, computeMemberScope(constructor, arguments))
+        return simpleType(annotations, constructor, arguments, nullable, computeMemberScope(constructor, arguments))
     }
 
     @JvmStatic
@@ -55,14 +55,21 @@ object KotlinTypeFactory {
             arguments: List<TypeProjection>,
             nullable: Boolean,
             memberScope: MemberScope
-    ): SimpleType = SimpleTypeImpl(annotations, constructor, arguments, nullable, memberScope)
+    ): SimpleType =
+            SimpleTypeImpl(constructor, arguments, nullable, memberScope)
+                    .let {
+                        if (annotations.isEmpty())
+                            it
+                        else
+                            AnnotatedSimpleType(it, annotations)
+                    }
 
     @JvmStatic
     fun simpleNotNullType(
             annotations: Annotations,
             descriptor: ClassDescriptor,
             arguments: List<TypeProjection>
-    ): SimpleType = SimpleTypeImpl(annotations, descriptor.typeConstructor, arguments, false, descriptor.getMemberScope(arguments))
+    ): SimpleType = simpleType(annotations, descriptor.typeConstructor, arguments, false, descriptor.getMemberScope(arguments))
 
     @JvmStatic
     fun simpleType(
@@ -82,17 +89,18 @@ object KotlinTypeFactory {
 }
 
 private class SimpleTypeImpl(
-        override val annotations: Annotations,
         override val constructor: TypeConstructor,
         override val arguments: List<TypeProjection>,
         override val isMarkedNullable: Boolean,
         override val memberScope: MemberScope
 ) : SimpleType() {
+    override val annotations: Annotations get() = Annotations.EMPTY
+
     override fun replaceAnnotations(newAnnotations: Annotations) =
-            if (newAnnotations === annotations)
+            if (newAnnotations.isEmpty())
                 this
             else
-                SimpleTypeImpl(newAnnotations, constructor, arguments, isMarkedNullable, memberScope)
+                AnnotatedSimpleType(this, newAnnotations)
 
     override fun makeNullableAsSpecified(newNullability: Boolean) =
             if (newNullability == isMarkedNullable)
@@ -100,7 +108,7 @@ private class SimpleTypeImpl(
             else if (newNullability)
                 NullableSimpleType(this)
             else
-                SimpleTypeImpl(annotations, constructor, arguments, newNullability, memberScope)
+                NotNullSimpleType(this)
 
     init {
         if (memberScope is ErrorUtils.ErrorScope) {
@@ -109,18 +117,30 @@ private class SimpleTypeImpl(
     }
 }
 
-private class NullableSimpleType(override val delegate: SimpleType) : DelegatingSimpleType() {
-    override val isMarkedNullable: Boolean
-        get() = true
-
+abstract class DelegatingSimpleTypeImpl(override val delegate: SimpleType) : DelegatingSimpleType() {
     override fun replaceAnnotations(newAnnotations: Annotations) =
-            if (newAnnotations !== delegate.annotations)
-                NullableSimpleType(delegate.replaceAnnotations(newAnnotations))
+            if (newAnnotations !== annotations)
+                AnnotatedSimpleType(this, newAnnotations)
             else
                 this
 
     override fun makeNullableAsSpecified(newNullability: Boolean): SimpleType {
-        if (newNullability) return this
-        return delegate.makeNullableAsSpecified(newNullability)
+        if (newNullability == isMarkedNullable) return this
+        return delegate.makeNullableAsSpecified(newNullability).replaceAnnotations(annotations)
     }
 }
+
+private class AnnotatedSimpleType(
+        delegate: SimpleType,
+        override val annotations: Annotations
+) : DelegatingSimpleTypeImpl(delegate)
+
+private class NullableSimpleType(delegate: SimpleType) : DelegatingSimpleTypeImpl(delegate) {
+    override val isMarkedNullable: Boolean
+        get() = true
+}
+
+private class NotNullSimpleType(delegate: SimpleType) : DelegatingSimpleTypeImpl(delegate) {
+    override val isMarkedNullable: Boolean
+        get() = false
+}