Various improvements to preferences code (#27710)

* Add isPostFlagged selector

* Remove unused code for actions_menu preferences

* Improve types of Preference and getPreference

* MM-58111 Change makeGetCategory to take category name once

* Use shouldShowJoinLeaveMessages everywhere

* Change makeGetCategory to better memoize its result

* Fix test that needs EnableJoinLeaveMessageByDefault to be set

* Remove more references to action_menu preferences

e2e-tests/cypress/tests/support/api/preference.js

@@ -256,17 +256,6 @@ Cypress.Commands.add('apiSaveCloudTrialBannerPreference', (userId, name, value)
     return cy.apiSaveUserPreference([preference], userId);
 });
 
-Cypress.Commands.add('apiSaveActionsMenuPreference', (userId, value = true) => {
-    const preference = {
-        user_id: userId,
-        category: 'actions_menu',
-        name: 'actions_menu_tutorial_state',
-        value: JSON.stringify({actions_menu_modal_viewed: value}),
-    };
-
-    return cy.apiSaveUserPreference([preference], userId);
-});
-
 Cypress.Commands.add('apiSaveStartTrialModal', (userId, value = 'true') => {
     const preference = {
         user_id: userId,
@@ -402,12 +391,6 @@ Cypress.Commands.add('apiDisableTutorials', (userId) => {
             name: userId,
             value: '999',
         },
-        {
-            user_id: userId,
-            category: 'actions_menu',
-            name: 'actions_menu_tutorial_state',
-            value: '{"actions_menu_modal_viewed":true}',
-        },
         {
             user_id: userId,
             category: 'drafts',