Write is_unsigned flag into metadata for an annotation arguments

Instead of adding new kind of types, we'll use flag to disambiguate
 usual types from unsigned ones, this approach has two advantages:
 - less changes in the metadata format
 - it allows naturally extend format for unsigned arrays,
  which will be supported later

 #KT-25310 Fixed
 #KT-25273 Fixed

compiler/testData/compileKotlinAgainstKotlin/unsignedTypesInAnnotations.kt

@@ -0,0 +1,21 @@
+// WITH_UNSIGNED
+
+// FILE: A.kt
+
+@kotlin.annotation.Target(AnnotationTarget.TYPE, AnnotationTarget.FUNCTION)
+annotation class Anno(val u: UInt)
+
+object ForTest {
+    @Anno(0u)
+    fun f(a: @Anno(43u) String) {}
+}
+
+// FILE: B.kt
+
+
+fun box(): String {
+    val result = (ForTest::f.annotations.first() as Anno).u // force annotation deserialization
+    if (result != 0u) return "Fail"
+
+    return "OK"
+}