[FIR] Add toString() methods to some ConeSubstitutor implementation

This is needed only for pleasant debugging

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

@@ -55,7 +55,11 @@ data class ConeStubTypeConstructor(
     val variable: ConeTypeVariable,
     val isTypeVariableInSubtyping: Boolean,
     val isForFixation: Boolean = false,
-) : TypeConstructorMarker
+) : TypeConstructorMarker {
+    override fun toString(): String {
+        return "Stub(${variable.typeConstructor.debugName})"
+    }
+}
 
 sealed class ConeStubType(val constructor: ConeStubTypeConstructor, override val nullability: ConeNullability) : StubTypeMarker,
     ConeSimpleKotlinType() {

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/substitution/Substitutors.kt

@@ -183,6 +183,10 @@ data class ChainedSubstitutor(private val first: ConeSubstitutor, private val se
         first.substituteOrNull(type)?.let { return second.substituteOrSelf(it) }
         return second.substituteOrNull(type)
     }
+
+    override fun toString(): String {
+        return "$first then $second"
+    }
 }
 
 fun ConeSubstitutor.chain(other: ConeSubstitutor): ConeSubstitutor {
@@ -220,6 +224,12 @@ class ConeSubstitutorByMap(
     }
 
     override fun hashCode() = hashCode
+
+    override fun toString(): String {
+        return substitution.entries.joinToString(prefix = "{", postfix = "}", separator = " | ") { (param, type) ->
+            "${param.name} -> ${type.renderForDebugging()}"
+        }
+    }
 }
 
 class ConeRawScopeSubstitutor(
@@ -292,6 +302,12 @@ internal class ConeTypeSubstitutorByTypeConstructor(
         val approximatedIntegerLiteralType = if (approximateIntegerLiterals) new.approximateIntegerLiteralType() else new
         return approximatedIntegerLiteralType.updateNullabilityIfNeeded(type)?.withCombinedAttributesFrom(type)
     }
+
+    override fun toString(): String {
+        return map.entries.joinToString(prefix = "{", postfix = "}", separator = " | ") { (constructor, type) ->
+            "$constructor -> ${type.renderForDebugging()}"
+        }
+    }
 }
 
 // Note: builder inference uses TypeSubstitutorByTypeConstructor for not fixed type substitution
@@ -304,6 +320,13 @@ class NotFixedTypeToVariableSubstitutorForDelegateInference(
         if (type.constructor.isTypeVariableInSubtyping) return null
         return bindings[type.constructor.variable].updateNullabilityIfNeeded(type)
     }
+
+    override fun toString(): String {
+        return bindings.entries.joinToString(prefix = "{", postfix = "}", separator = " | ") { (variable, type) ->
+            require(variable is ConeTypeVariable)
+            "TV(${variable.typeConstructor.debugName}) -> ${type.renderForDebugging()}"
+        }
+    }
 }
 
 class ConeStubAndTypeVariableToErrorTypeSubstitutor(
@@ -328,6 +351,10 @@ class ConeStubAndTypeVariableToErrorTypeSubstitutor(
             else -> null
         }
     }
+
+    override fun toString(): String {
+        return "{<Stub type> -> <Error type>}"
+    }
 }
 
 fun ConeSubstitutor.replaceStubsAndTypeVariablesToErrors(

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/resolve/calls/TypeVariableTypeRemovingSubstitutor.kt

@@ -30,4 +30,8 @@ private class TypeVariableTypeRemovingSubstitutor(typeContext: ConeTypeContext)
         }
         return ConeErrorType(ConeUnknownLambdaParameterTypeDiagnostic())
     }
+
+    override fun toString(): String {
+        return "{<Type variable> -> <Error type>}"
+    }
 }