[MM-62973][MM-63028][MM-63034][MM-63027] Various accessibility fixes around Browse Channels modal (#30922)

* [MM-62973] Fix order of Close button and other buttons in the header

* [MM-63028] Add aria-live status area when searching for channels

* [MM-63027] Add announcement that channel is joined

* [MM-63034] Add role=checkbox and reformat HTML to have correct custom checkbox code

* Update snapshots from generic_modal change

* PR feedback

* PR feedback

* PR feedback

e2e-tests/cypress/tests/integration/channels/enterprise/accessibility/accessibility_modals_dialogs_spec.ts

@@ -120,8 +120,8 @@ describe('Verify Accessibility Support in Modals & Dialogs', () => {
                     // # Hide already joined channels
                     cy.findByText('Hide Joined').click();
 
-                    // # Focus on the Create Channel button and TAB four time
-                    cy.get('#createNewChannelButton').focus().tab().tab().tab().tab();
+                    // # Focus on the Create Channel button and TAB five time
+                    cy.get('#createNewChannelButton').focus().tab().tab().tab().tab().tab();
 
                     // * Verify channel name is highlighted and reader reads the channel name and channel description
                     cy.get('#moreChannelsList').within(() => {