MM-59854 Fully allow at mentions in message attachment field values and add E2E tests (#28018)

* Add descriptions to test cases for getNeededAtMentionedUsernames

* MM-59854 Load users who are at-mentioned in message attachment fields

* MM-59854 Add server support for at-mentioning users in message attachment fields

* Migrate support/external_commands from JS to TS

* MM-59584 Ensure that at-mentions never show in other message attachment fields

* MM-59584 Add E2E tests for how we load users based on at mentions

* Use new E2E test helpers in other places

* Update snapshots

e2e-tests/cypress/tests/integration/channels/channel/user_to_admin_updates_manage_channel_members_rhs_spec.js

@@ -10,11 +10,7 @@
 // Stage: @prod
 // Group: @channels @channel
 
-import {getAdminAccount} from '../../../support/env';
-
 describe('View Members modal', () => {
-    const sysadmin = getAdminAccount();
-
     it('MM-20164 - Going from a Member to an Admin should update the modal', () => {
         cy.apiInitSetup().then(({team, user}) => {
             cy.apiCreateUser().then(({user: user1}) => {
@@ -24,27 +20,19 @@ describe('View Members modal', () => {
             // # Promote user as a system admin
             // # Visit default channel and verify members modal
             cy.apiLogin(user);
-            promoteToSysAdmin(user, sysadmin);
+            cy.externalUpdateUserRoles(user.id, 'system_user system_admin');
             cy.visit(`/${team.name}/channels/town-square`);
             verifyMemberDropdownAction(true);
 
             // # Make user a regular member
             // # Reload and verify members modal
-            demoteToMember(user, sysadmin);
+            cy.externalUpdateUserRoles(user.id, 'system_user');
             cy.reload();
             verifyMemberDropdownAction(false);
         });
     });
 });
 
-const demoteToMember = (user, sysadmin) => {
-    cy.externalRequest({user: sysadmin, method: 'put', path: `users/${user.id}/roles`, data: {roles: 'system_user'}});
-};
-
-const promoteToSysAdmin = (user, sysadmin) => {
-    cy.externalRequest({user: sysadmin, method: 'put', path: `users/${user.id}/roles`, data: {roles: 'system_user system_admin'}});
-};
-
 function verifyMemberDropdownAction(hasActionItem) {
     // # Click member count to open member rhs
     cy.get('#member_rhs').click();

e2e-tests/cypress/tests/integration/channels/channel/user_to_channel_admin_member_updates_manage_channel_members_rhs_spec.js

@@ -11,10 +11,6 @@
 
 import {getAdminAccount} from '../../../support/env';
 
-const demoteToMember = (user, admin) => {
-    cy.externalRequest({user: admin, method: 'put', path: `users/${user.id}/roles`, data: {roles: 'system_user'}});
-};
-
 const demoteToChannelMember = (user, channelId, admin) => {
     cy.externalRequest({
         user: admin,
@@ -70,7 +66,7 @@ describe('Change Roles', () => {
             cy.visit(`/${team.name}/channels/${channel.name}`);
 
             // # Make user a regular member for channel and system
-            demoteToMember(testUser, admin);
+            cy.externalUpdateUserRoles(user.id, 'system_user');
             demoteToChannelMember(testUser, testChannelId, admin);
 
             // # Reload page to ensure no cache or saved information