psi2ir: support unsigned integer literals

NB in FE unsigned integer constants are now represented using signed
integer types (e.g., UInt constant actually holds an Int value).
So, in IR so far we also represent unsigned constant literals as
constant values of corresponding signed types, but with corresponding
unsigned type:
0xFFFF_FFFFu becomes 'CONST Int type=kotlin.UInt value=-1'

compiler/tests-common/tests/org/jetbrains/kotlin/ir/AbstractIrGeneratorTestCase.kt

@@ -51,6 +51,7 @@ abstract class AbstractIrGeneratorTestCase : CodegenTestCase() {
         val javacOptions = ArrayList<String>(0)
         var addRuntime = false
         var addReflect = false
+        var addUnsigned = false
         for (file in files) {
             if (InTextDirectivesUtils.isDirectiveDefined(file.content, "WITH_RUNTIME")) {
                 addRuntime = true
@@ -58,6 +59,9 @@ abstract class AbstractIrGeneratorTestCase : CodegenTestCase() {
             if (InTextDirectivesUtils.isDirectiveDefined(file.content, "WITH_REFLECT")) {
                 addReflect = true
             }
+            if (InTextDirectivesUtils.isDirectiveDefined(file.content, "WITH_UNSIGNED")) {
+                addUnsigned = true
+            }
 
             javacOptions.addAll(InTextDirectivesUtils.findListWithPrefixes(file.content, "// JAVAC_OPTIONS:"))
         }
@@ -65,6 +69,7 @@ abstract class AbstractIrGeneratorTestCase : CodegenTestCase() {
         val configurationKind = when {
             addReflect -> ConfigurationKind.ALL
             addRuntime -> ConfigurationKind.NO_KOTLIN_REFLECT
+            addUnsigned -> ConfigurationKind.WITH_UNSIGNED_TYPES
             else -> ConfigurationKind.JDK_ONLY
         }