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/serialization/src/org/jetbrains/kotlin/serialization/AnnotationSerializer.kt

@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.descriptors.annotations.AnnotationDescriptor
 import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.ProtoBuf.Annotation.Argument.Value
 import org.jetbrains.kotlin.metadata.ProtoBuf.Annotation.Argument.Value.Type
+import org.jetbrains.kotlin.metadata.deserialization.Flags
 import org.jetbrains.kotlin.resolve.constants.*
 import org.jetbrains.kotlin.resolve.descriptorUtil.annotationClass
 import org.jetbrains.kotlin.types.ErrorUtils
@@ -127,21 +128,25 @@ class AnnotationSerializer(private val stringTable: DescriptorAwareStringTable)
             override fun visitUByteValue(value: UByteValue, data: Unit?) {
                 type = Type.BYTE
                 intValue = value.value.toLong()
+                flags = Flags.IS_UNSIGNED.toFlags(true)
             }
 
             override fun visitUShortValue(value: UShortValue, data: Unit?) {
                 type = Type.SHORT
                 intValue = value.value.toLong()
+                flags = Flags.IS_UNSIGNED.toFlags(true)
             }
 
             override fun visitUIntValue(value: UIntValue, data: Unit?) {
                 type = Type.INT
                 intValue = value.value.toLong()
+                flags = Flags.IS_UNSIGNED.toFlags(true)
             }
 
             override fun visitULongValue(value: ULongValue, data: Unit?) {
                 type = Type.LONG
                 intValue = value.value
+                flags = Flags.IS_UNSIGNED.toFlags(true)
             }
         }, Unit)
     }