[FIR] Don't enhance Int and String Java final static fields

It's effectively a breaking change (^KT-62558)

K2 assigns flexible type to all static fields (from Java) and, for example,
`String? becomes String unlike K1. It affects IR signature generating.
That's why signature dump is disabled for some tests.

^KT-57811 Fixed
^KT-61786 Fixed

compiler/fir/analysis-tests/testData/resolve/inference/noEnhancementOnFinalStaticConstFields.kt

@@ -0,0 +1,15 @@
+// ISSUE: KT-57811, KT-61786
+
+// FILE: JavaClass.java
+
+public class JavaClass {
+    public static final String X = null;
+}
+
+// FILE: main.kt
+
+fun test(x1: String?): String {
+    val x: String?
+    x = x1 ?: JavaClass.X
+    return x
+}