Native assets: package in framework on iOS and MacOS (#140907)

Packages the native assets for iOS and MacOS in frameworks.

Issue:

* https://github.com/flutter/flutter/issues/140544
* https://github.com/flutter/flutter/issues/129757

## Details

* [x] This packages dylibs from the native assets feature in frameworks. It packages every dylib in a separate framework.
* [x] The dylib name is updated to use `@rpath` instead of `@executable_path`.
* [x] The dylibs for flutter-tester are no longer modified to change the install name. (Previously it was wrongly updating the install name to the location the dylib would have once deployed in an app.)
* [x] Use symlinking on MacOS.

dev/devicelab/bin/tasks/module_test_ios.dart

@@ -250,9 +250,7 @@ dependencies:
       checkDirectoryNotExists(path.join(ephemeralIOSHostApp.path, 'Frameworks', '$dartPluginName.framework'));
 
       // Native assets embedded, no embedded framework.
-      const String libFfiPackageDylib = 'lib$ffiPackageName.dylib';
-      checkFileExists(path.join(ephemeralIOSHostApp.path, 'Frameworks', libFfiPackageDylib));
-      checkDirectoryNotExists(path.join(ephemeralIOSHostApp.path, 'Frameworks', '$ffiPackageName.framework'));
+      checkFileExists(path.join(ephemeralIOSHostApp.path, 'Frameworks', '$ffiPackageName.framework', ffiPackageName));
 
       section('Clean and pub get module');
 
@@ -385,7 +383,8 @@ end
 
       checkFileExists(path.join(
         hostFrameworksDirectory,
-        libFfiPackageDylib,
+        '$ffiPackageName.framework',
+        ffiPackageName,
       ));
 
       section('Check the NOTICE file is correct');
@@ -491,7 +490,8 @@ end
         checkFileExists(path.join(
           archivedAppPath,
           'Frameworks',
-          libFfiPackageDylib,
+          '$ffiPackageName.framework',
+          ffiPackageName,
         ));
 
         // The host app example builds plugins statically, url_launcher_ios.framework