[kernel] Move util.dart from bin to lib.

bin/util.dart doesn't have main() entry point and that breaks snapshot generation that is
automatically invoked by pub for all dart sources in bin/ folder.

See https://github.com/flutter/flutter/pull/19044\#issuecomment-402241782

Change-Id: Ie91549173536740992ce61d830efdfdc603c5564
Reviewed-on: https://dart-review.googlesource.com/63683
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

pkg/kernel/bin/count_breakdown.dart

@@ -5,7 +5,7 @@
 
 import 'dart:io';
 import 'package:kernel/kernel.dart';
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Enumerates the different node types in the provided dill file");

pkg/kernel/bin/dump.dart

@@ -6,8 +6,7 @@
 import 'dart:io';
 
 import 'package:kernel/kernel.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Prints a dill file as a textual format.");

pkg/kernel/bin/eval.dart

@@ -7,8 +7,7 @@ import 'dart:io';
 
 import 'package:kernel/kernel.dart';
 import 'package:kernel/interpreter/interpreter.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Interpreter for a dill file.");

pkg/kernel/bin/size_breakdown.dart

@@ -7,8 +7,7 @@ import 'dart:io';
 
 import 'package:kernel/kernel.dart';
 import 'package:kernel/binary/ast_from_binary.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Gives an overview of which parts of the dill file");

pkg/kernel/bin/split.dart

@@ -10,8 +10,7 @@ import 'package:kernel/ast.dart';
 import 'package:kernel/binary/ast_to_binary.dart';
 import 'package:kernel/binary/limited_ast_to_binary.dart';
 import 'package:kernel/kernel.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Split a dill file into separate dill files (one library per file).");

pkg/kernel/bin/transform.dart

@@ -21,8 +21,7 @@ import 'package:kernel/transformations/treeshaker.dart' as treeshaker;
 // import 'package:kernel/verifier.dart';
 import 'package:kernel/transformations/coq.dart' as coq;
 import 'package:kernel/vm/constants_native_effects.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 ArgParser parser = new ArgParser()
   ..addOption('format',

pkg/kernel/bin/type_check.dart

@@ -7,8 +7,7 @@ import 'dart:io';
 
 import 'package:kernel/error_formatter.dart';
 import 'package:kernel/naive_type_checker.dart';
-
-import 'util.dart';
+import 'package:kernel/src/tool/command_line_util.dart';
 
 void usage() {
   print("Type checker that can be used to find strong mode");