Set --debugger-module-names to true by default in preparation for removal of the flag

first step for resolving #42104

Change-Id: Ie385e1d014149d67c5223aef698132b67df7ee43
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153949
Reviewed-by: Jonah Williams <jonahwilliams@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Anna Gringauze <annagrin@google.com>

Author: Anna Gringauze

pkg/frontend_server/lib/frontend_server.dart

@@ -175,7 +175,7 @@ ArgParser argParser = ArgParser(allowTrailingOptions: true)
   ..addOption('libraries-spec',
       help: 'A path or uri to the libraries specification JSON file')
   ..addFlag('debugger-module-names',
-      help: 'Use debugger-friendly modules names', defaultsTo: false)
+      help: 'Use debugger-friendly modules names', defaultsTo: true)
   ..addFlag('experimental-emit-debug-metadata',
       help: 'Emit module and library metadata for the debugger',
       defaultsTo: false)

pkg/frontend_server/test/frontend_server_test.dart

@@ -1490,7 +1490,6 @@ true
         '--output-dill=${dillFile.path}',
         '--target=dartdevc',
         '--packages=${tempDir.path}/.packages',
-        '--debugger-module-names'
       ];
 
       final StreamController<List<int>> streamController =
@@ -1557,7 +1556,6 @@ true
         '--output-dill=${dillFile.path}',
         '--target=dartdevc',
         '--packages=${tempDir.path}/.packages',
-        '--debugger-module-names',
         '--experimental-emit-debug-metadata'
       ];
 
@@ -1621,7 +1619,6 @@ true
         '--output-dill=${dillFile.path}',
         '--target=dartdevc',
         '--packages=${tempDir.path}/.packages',
-        '--debugger-module-names'
       ];
 
       final StreamController<List<int>> streamController =
@@ -1729,7 +1726,6 @@ true
         '--output-dill=${dillFile.path}',
         '--target=dartdevc',
         '--packages=${tempDir.path}/.packages',
-        '--debugger-module-names'
       ];
 
       final StreamController<List<int>> streamController =