Unbind general FirDiagnostic from PsiFile & PsiElement

compiler/frontend.common/src/org/jetbrains/kotlin/diagnostics/GenericDiagnostics.kt

@@ -0,0 +1,14 @@
+/*
+ * 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.diagnostics
+
+interface GenericDiagnostics<T : UnboundDiagnostic> : Iterable<T> {
+    fun all(): Collection<T>
+
+    fun isEmpty(): Boolean = all().isEmpty()
+
+    override fun iterator(): Iterator<T> = all().iterator()
+}