Added missing specificity comparator to FIR

This is required to correctly resolve overloading in cases when we
need to find most specific alternative in Java between int and Integer.

compiler/fir/analysis-tests/testData/resolveWithStdlib/j+k/FlexiblePrimitiveOverloading.kt

@@ -0,0 +1,6 @@
+// FULL_JDK
+import java.lang.Integer.getInteger
+
+fun foo() {
+    getInteger("text", 239)
+}

compiler/fir/analysis-tests/testData/resolveWithStdlib/j+k/FlexiblePrimitiveOverloading.txt

@@ -0,0 +1,4 @@
+FILE: FlexiblePrimitiveOverloading.kt
+    public final fun foo(): R|kotlin/Unit| {
+        R|java/lang/Integer.getInteger|(String(text), Int(239))
+    }