[dart2js] Change --(no-)null-safety to --(no-)sound-null-safety.

Change-Id: I18d9cb237ba1bafda1a0f3cdc64fe43c22889311
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/148222
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Commit-Queue: Mayank Patke <fishythefish@google.com>

pkg/compiler/lib/src/commandline_options.dart

@@ -98,8 +98,8 @@ class Flags {
 
   static const String serverMode = '--server-mode';
 
-  static const String nullSafety = '--null-safety';
-  static const String noNullSafety = '--no-null-safety';
+  static const String nullSafety = '--sound-null-safety';
+  static const String noNullSafety = '--no-sound-null-safety';
 
   static const String newDeferredSplit = '--new-deferred-split';
   static const String reportInvalidInferredDeferredTypes =

tools/bots/test_matrix.json

@@ -637,7 +637,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--no-null-safety"
+          "--no-sound-null-safety"
         ],
         "use-sdk": true
       }
@@ -708,7 +708,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--no-null-safety",
+          "--no-sound-null-safety",
           "--libraries-spec=sdk_nnbd/lib/libraries.json",
           "--platform-binaries=out/ReleaseX64/"
         ],
@@ -723,7 +723,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--no-null-safety",
+          "--no-sound-null-safety",
           "--libraries-spec=sdk_nnbd/lib/libraries.json",
           "--platform-binaries=xcodebuild/ReleaseX64/"
         ],
@@ -738,7 +738,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--null-safety",
+          "--sound-null-safety",
           "--libraries-spec=sdk_nnbd/lib/libraries.json",
           "--platform-binaries=out/ReleaseX64/"
         ],
@@ -753,7 +753,7 @@
           "non-nullable"
         ],
         "dart2js-options": [
-          "--null-safety",
+          "--sound-null-safety",
           "--libraries-spec=sdk_nnbd/lib/libraries.json",
           "--platform-binaries=xcodebuild/ReleaseX64/"
         ],