FIR IDE: add action to override/implement missing members

This commit adds the following actions:

- quickfix to implement missing members
- quickfix to implement missing members as constructor parameters
- action to implement members (Code - Generate - Implement)
- action to override members (Code - Generate - Override)

The current implementation is still missing some pieces, which will be
addressed in future changes.

- fully qualified names are not shorten
- some Kotlin types are not rendered correctly

core/compiler.common/src/org/jetbrains/kotlin/util/ImplementationStatus.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2010-2021 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.util
+
+/** Implementation status of a member symbol that is available inside a class scope. */
+enum class ImplementationStatus {
+    /** This symbol is not implemented and should be implemented if the class is not abstract. */
+    NOT_IMPLEMENTED,
+
+    /** The symbol is inheriting multiple non-abstract symbols and hence must be explicitly implemented. */
+    AMBIGUOUSLY_INHERITED,
+
+    /**
+     * This symbol has an inherited implementation, and it can be overridden if desired. For example, it's an open non-abstract member or
+     * it's automatically synthesized by the Kotlin compiler.
+     */
+    INHERITED_OR_SYNTHESIZED,
+
+    /** The symbol is already implemented in this class. */
+    ALREADY_IMPLEMENTED,
+
+    /**
+     * The symbol is not implemented in the class and it cannot be implemented. For example, it's final in super classes or the current
+     * class is `expect`.
+     */
+    CANNOT_BE_IMPLEMENTED;
+
+    val shouldBeImplemented: Boolean get() = this == NOT_IMPLEMENTED || this == AMBIGUOUSLY_INHERITED
+    val isOverridable: Boolean get() = this != ALREADY_IMPLEMENTED && this != CANNOT_BE_IMPLEMENTED
+}
+