[FIR] KT-57568: Make K2 treat signed ints as more specific than unsigned

This is the way it works in K1.
See `OverloadingConflictResolver.kt:345`.

^KT-57568 Fixed

Merge-request: KT-MR-9395
Merged-by: Nikolay Lunyak <Nikolay.Lunyak@jetbrains.com>

compiler/testData/diagnostics/testsWithStdLib/ambiguityWithUnsignedSpecificity.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// ISSUE: KT-57568
+
+fun <T, K> T.convert(): K = null!!
+
+fun of(size: ULong) {
+    of(size.convert())
+}
+
+fun of(size: Int) {}
+
+fun of(size: Long) {}