Improve types of testing utilities and fix some types in unit test code (#26122)

* Improve type of DeepPartial and make mergeObjects handle Sets/Maps properly

* Fix linting

* Remove undefined fields from menu_cloud_trial.test

* Prevent importing the wrong version of DeepPartial

webapp/channels/src/components/admin_console/license_settings/modals/confirm_license_removal_modal.test.tsx

@@ -24,7 +24,7 @@ describe('components/admin_console/license_settings/modals/confirm_license_remov
             modals: {
                 modalState: {
                     confirm_license_removal: {
-                        open: 'true',
+                        open: true,
                     },
                 },
             },

webapp/channels/src/components/admin_console/license_settings/modals/upload_license_modal.test.tsx

@@ -44,7 +44,7 @@ describe('components/admin_console/license_settings/modals/upload_license_modal'
             modals: {
                 modalState: {
                     upload_license: {
-                        open: 'true',
+                        open: true,
                     },
                 },
             },