reduce usage of Utils.localizeMessage (#29282)

* reduce usage of Utils.localizeMessage

As we begin to transition to react-intl's `formatjs` for extraction, our custom wrappers like `Utils.localizeMessage` prevent an adoption roadblock.

This is the first in a series of PRs to begin to migrate away in favour of:
* `useIntl` when inside React functional component
* use `injectIntl` and use access the `intl` prop from class components
* use the new `getIntl`, leveraging a memoized `createIntl` and the store outside of React components

I'm pausing in this effort to get a feel from peers on both the substance of these changes and best practices in supporting them.

* prefer shallowWithIntl, renderWithContext, and local injectIntl wrapping

* revert unintentional whitespaces

* clarify getIntl, add minor unit test

* avoid triggering mmjstool

* update e2e tests

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

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

@@ -181,7 +181,7 @@ describe('Verify Accessibility Support in Post', () => {
                 }
 
                 // * Verify focus is on the reactions button
-                cy.get(`#CENTER_reaction_${postId}`).should('be.focused').and('have.attr', 'aria-label', 'add reaction');
+                cy.get(`#CENTER_reaction_${postId}`).should('be.focused').and('have.attr', 'aria-label', 'Add Reaction');
                 cy.focused().tab();
 
                 // * Verify focus is on the save post button
@@ -247,7 +247,7 @@ describe('Verify Accessibility Support in Post', () => {
                 cy.focused().tab({shift: true});
 
                 // * Verify focus is on the reactions button
-                cy.get(`#RHS_COMMENT_reaction_${postId}`).should('be.focused').and('have.attr', 'aria-label', 'add reaction');
+                cy.get(`#RHS_COMMENT_reaction_${postId}`).should('be.focused').and('have.attr', 'aria-label', 'Add Reaction');
                 cy.focused().tab({shift: true});
 
                 // * Verify focus is on most recent action