[IR] Dump IdSignatures and mangled names in irText tests

The reason #1 for this feature is that we want to test IdSignatures
generated for declarations. Currently, there is no (easy) way to ensure
that a change in the signature building logic doesn't cause any breaking
changes wrt klibs.

Now, most IdSignatures include hashed mangled names in them, so even if
we catch a regression where the included hash changes, there would be no
way of knowing immediately what caused it, unless we'd also have mangled
names in the expectations.

The reason #2 is to test the manglers themselves. Currently, there are
no tests for them. They heavily duplicate each other, this is already
causing issues (see KT-57427) that would be very hard to catch without
these tests.

^KT-58238 Fixed

compiler/testData/ir/irText/classes/companionObject.sig.kt.txt

@@ -0,0 +1,44 @@
+// CHECK:
+//   Mangled name: Test1
+//   Public signature: /Test1|null[0]
+class Test1 {
+  // CHECK:
+  //   Mangled name: Test1.Companion
+  //   Public signature: /Test1.Companion|null[0]
+  companion object Companion {
+    // CHECK:
+    //   Mangled name: Test1.Companion#<init>(){}
+    //   Public signature: /Test1.Companion.<init>|-5645683436151566731[0]
+    private constructor() /* primary */
+
+  }
+
+  // CHECK:
+  //   Mangled name: Test1#<init>(){}
+  //   Public signature: /Test1.<init>|-5645683436151566731[0]
+  constructor() /* primary */
+
+}
+
+// CHECK:
+//   Mangled name: Test2
+//   Public signature: /Test2|null[0]
+class Test2 {
+  // CHECK:
+  //   Mangled name: Test2.Named
+  //   Public signature: /Test2.Named|null[0]
+  companion object Named {
+    // CHECK:
+    //   Mangled name: Test2.Named#<init>(){}
+    //   Public signature: /Test2.Named.<init>|-5645683436151566731[0]
+    private constructor() /* primary */
+
+  }
+
+  // CHECK:
+  //   Mangled name: Test2#<init>(){}
+  //   Public signature: /Test2.<init>|-5645683436151566731[0]
+  constructor() /* primary */
+
+}
+