[FIR] Add lValueTypeRef to FirVariableAssignment, fix tests with ASSIGNMENT_TYPE_MISMATCH

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/ImplementationConfigurator.kt

@@ -495,5 +495,14 @@ object ImplementationConfigurator : AbstractFirTreeImplementationConfigurator()
             default(it, "FirImplicitTypeRefImpl(null)")
             useTypes(implicitTypeRefType)
         }
+
+        configureFieldInAllImplementations(
+            field = "lValueTypeRef",
+            implementationPredicate = { it.type in "FirVariableAssignmentImpl" },
+            fieldPredicate = { it.defaultValueInImplementation == null }
+        ) {
+            default(it, "FirImplicitTypeRefImpl(null)")
+            useTypes(implicitTypeRefType)
+        }
     }
 }

compiler/fir/tree/tree-generator/src/org/jetbrains/kotlin/fir/tree/generator/NodeConfigurator.kt

@@ -521,6 +521,7 @@ object NodeConfigurator : AbstractFieldConfigurator<FirTreeBuilder>(FirTreeBuild
 
         variableAssignment.configure {
             +field("lValue", reference)
+            +field("lValueTypeRef", typeRef).withReplace()
             +field("rValue", expression).withTransform()
         }