[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/expressions/funInterface/samConversionInVarargsMixed.sig.kt.txt

@@ -0,0 +1,22 @@
+// CHECK:
+//   Mangled name: MyRunnable
+//   Public signature: /MyRunnable|null[0]
+fun interface MyRunnable {
+
+  // CHECK:
+  //   Mangled name: MyRunnable#run(){}
+  //   Public signature: /MyRunnable.run|-991178076551934874[0]
+  abstract fun run(): Unit
+
+}
+
+// CHECK:
+//   Mangled name: #foo(kotlin.Array<out|MyRunnable>...){}
+//   Public signature: /foo|6689815842309055774[0]
+fun foo(vararg rs: MyRunnable): Unit
+
+// CHECK:
+//   Mangled name: #test(kotlin.Any;MyRunnable){}
+//   Public signature: /test|-2252565057874021036[0]
+fun test(a: Any, r: MyRunnable): Unit
+