Revert extention -> extension change

"EXTENTION" is used for bootstrapping in the build_runner which
will need to change for this change.

Author: srujzs

dwds/lib/src/handlers/injector.dart

@@ -18,7 +18,7 @@ import 'package:shelf/shelf.dart';
 const bootstrapJsExtension = '.bootstrap.js';
 
 /// Marker placed by build_web_compilers for where to put injected JS code.
-const entrypointExtensionMarker = '/* ENTRYPOINT_EXTENSION_MARKER */';
+const entrypointExtensionMarker = '/* ENTRYPOINT_EXTENTION_MARKER */';
 
 /// Marker placed by build_web_compilers for where to put injected JS code.
 const mainExtensionMarker = '/* MAIN_EXTENSION_MARKER */';

frontend_server_client/lib/src/dartdevc_bootstrap_amd.dart

@@ -48,7 +48,7 @@ document.head.appendChild(requireEl);
 /// `foo__bar__baz`. Rather than attempt to guess, we assume the first property of
 /// this object is the module.
 String generateAmdMainModule({required String entrypoint}) {
-  return '''/* ENTRYPOINT_EXTENSION_MARKER */
+  return '''/* ENTRYPOINT_EXTENTION_MARKER */
 // Create the main module loaded below.
 require(["$entrypoint.lib.js", "dart_sdk"], function(app, dart_sdk) {
   dart_sdk.dart.setStartAsyncSynchronously(true);

frontend_server_common/lib/src/bootstrap.dart

@@ -122,7 +122,7 @@ document.head.appendChild(requireEl);
 /// `foo__bar__baz`. Rather than attempt to guess, we assume the first property of
 /// this object is the module.
 String generateMainModule({required String entrypoint}) {
-  return '''/* ENTRYPOINT_EXTENSION_MARKER */
+  return '''/* ENTRYPOINT_EXTENTION_MARKER */
 
 // Create the main module loaded below.
 define("main_module.bootstrap", ["$entrypoint", "dart_sdk"], function(app, dart_sdk) {
@@ -357,7 +357,7 @@ $_simpleLoaderScript
 String generateDDCMainModule(
     {required String entrypoint, String? exportedMain}) {
   final exportedMainName = exportedMain ?? entrypoint.split('.')[0];
-  return '''/* ENTRYPOINT_EXTENSION_MARKER */
+  return '''/* ENTRYPOINT_EXTENTION_MARKER */
 
 (function() {
   let appName = "$entrypoint";
@@ -453,7 +453,7 @@ $_simpleLoaderScript
 }
 
 String generateDDCLibraryBundleMainModule({required String entrypoint}) {
-  return '''/* ENTRYPOINT_EXTENSION_MARKER */
+  return '''/* ENTRYPOINT_EXTENTION_MARKER */
 
 (function() {
   let appName = "org-dartlang-app:///$entrypoint";