Directly search in IrClass for declarations to fill bodies with plugin

because some other compiler plugins (Compose) copy/rewrite IR declarations
completely, and in the end, functions that are present in the final IR tree
do not have bodies.

Correctly create IrProperty and IrField when they were absent from the
descriptors (in case for private serializer properties)

Do not use symbol table because 'declare' API is not available in plugins.

Fixes https://github.com/JetBrains/compose-jb/issues/46

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt

@@ -1,17 +1,6 @@
 /*
- * Copyright 2010-2017 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.ir.util