[FIR] Introduce ConeDynamicType

compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/ConeTypes.kt

@@ -80,9 +80,9 @@ open class ConeFlexibleType(
 
     final override fun equals(other: Any?): Boolean {
         if (this === other) return true
-        if (javaClass != other?.javaClass) return false
-
-        other as ConeFlexibleType
+        // I suppose dynamic type (see below) and flexible type should use the same equals,
+        // because ft<Any?, Nothing> should never be created
+        if (other !is ConeFlexibleType) return false
 
         if (lowerBound != other.lowerBound) return false
         if (upperBound != other.upperBound) return false
@@ -97,6 +97,16 @@ open class ConeFlexibleType(
     }
 }
 
+@RequiresOptIn(message = "Please use ConeDynamicType.create instead")
+annotation class DynamicTypeConstructor
+
+class ConeDynamicType @DynamicTypeConstructor constructor(
+    lowerBound: ConeSimpleKotlinType,
+    upperBound: ConeSimpleKotlinType
+) : ConeFlexibleType(lowerBound, upperBound), DynamicTypeMarker {
+    companion object
+}
+
 fun ConeSimpleKotlinType.unwrapDefinitelyNotNull(): ConeSimpleKotlinType {
     return when (this) {
         is ConeDefinitelyNotNullType -> original

compiler/fir/cones/src/org/jetbrains/kotlin/fir/types/TypeRenderer.kt

@@ -30,6 +30,11 @@ fun ConeKotlinType.render(): String {
         is ConeLookupTagBasedType -> {
             "${renderAttributes()}${lookupTag.name.asString()}"
         }
+        is ConeDynamicType -> {
+            buildString {
+                append("dynamic")
+            }
+        }
         is ConeFlexibleType -> {
             buildString {
                 append("ft<")