[MM-61598]: Fix ARIA roles, states, and properties are valid in user profile image and @user buttons (#29692)

* [MA-26]: Fix ARIA roles, states, and properties are valid in user profile image and @user buttons

* [MA-26]: Remove irrelevant e2e tests

* [MA-26]: Remove nested interactive elements

* [MA-26]: Updated mention-link styles

* Minor change

---------

Co-authored-by: ayush-chauhan233 <ayush.chauhan@brightscout.com>

e2e-tests/cypress/tests/integration/channels/accessibility/accessibility_keyboard_usability_spec.js

@@ -156,8 +156,6 @@ describe('Verify Accessibility keyboard usability across different regions in th
                 cy.get(region).should('have.attr', 'role', 'application');
             });
             cy.get('.search__form').should('have.attr', 'role', 'search');
-            cy.get(`#post_${postId}`).children('.post__content').eq(0).should('have.attr', 'role', 'application');
-            cy.get(`#rhsPost_${postId}`).children('.post__content').eq(0).should('have.attr', 'role', 'application');
         });
     });
 });

e2e-tests/cypress/tests/integration/channels/accessibility/accessibility_post_spec.js

@@ -162,7 +162,7 @@ describe('Verify Accessibility Support in Post', () => {
         cy.getLastPostId().then((postId) => {
             cy.get(`#post_${postId}`).within(() => {
                 // * Verify focus is on profile image
-                cy.get('.status-wrapper button').first().should('be.focused');
+                cy.get('button.status-wrapper').first().should('be.focused');
                 cy.focused().tab();
 
                 // * Verify focus is on the username