feat(Escaped Identifiers): add ability to use any symbol wrapped in back ticks.

js/js.translator/testData/box/escapedIdentifiers/topLevelLocalCompanionMangling.kt

@@ -0,0 +1,23 @@
+// IGNORE_BACKEND: JS
+// !LANGUAGE: +JsAllowInvalidCharsIdentifiersEscaping
+
+package foo
+
+class class_with_invalid_chars {
+    companion object {
+        fun foo(): Int = 23
+    }
+}
+
+class `class@with$invalid chars` {
+    companion object {
+        fun foo(): Int = 42
+    }
+}
+
+fun box(): String {
+    assertEquals(23, class_with_invalid_chars.foo())
+    assertEquals(42, `class@with$invalid chars`.foo())
+
+    return "OK"
+}