Minor: Extract code for checking Dalvik identifiers to frontend

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/dalvikIdentifierUtils.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+@file:JvmName("DalvikIdentifierUtils")
+package org.jetbrains.kotlin.resolve.jvm.checkers
+
+fun isValidDalvikIdentifier(identifier: String) = identifier.all { isValidDalvikCharacter(it) }
+
+// https://source.android.com/devices/tech/dalvik/dex-format.html#string-syntax
+private fun isValidDalvikCharacter(c: Char) = when (c) {
+    in 'A'..'Z' -> true
+    in 'a'..'z' -> true
+    in '0'..'9' -> true
+    '$', '-', '_' -> true
+    in '\u00a1' .. '\u1fff' -> true
+    in '\u2010' .. '\u2027' -> true
+    in '\u2030' .. '\ud7ff' -> true
+    in '\ue000' .. '\uffef' -> true
+    else -> false
+}