FIR2IR: use invariant projections for SAM_CONVERSION types

compiler/testData/ir/irText/firProblems/kt19251.kt

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+// FULL_JDK
+// FILE: Fun.java
+public interface Fun {
+    String invoke(String string);
+}
+
+// FILE: test.kt
+fun box(): String {
+    val map = mutableMapOf<Fun, String>()
+    val fn = Fun { TODO() }
+    return map.computeIfAbsent(fn, { "OK" })
+}
+