Add canonical link tags in web UI (#25715)

app/javascript/mastodon/features/account/components/header.jsx

@@ -476,6 +476,7 @@ class Header extends ImmutablePureComponent {
         <Helmet>
           <title>{titleFromAccount(account)}</title>
           <meta name='robots' content={(isLocal && isIndexable) ? 'all' : 'noindex'} />
+          <link rel='canonical' href={account.get('url')} />
         </Helmet>
       </div>
     );

app/javascript/mastodon/features/status/index.jsx

@@ -716,6 +716,7 @@ class Status extends ImmutablePureComponent {
         <Helmet>
           <title>{titleFromStatus(intl, status)}</title>
           <meta name='robots' content={(isLocal && isIndexable) ? 'all' : 'noindex'} />
+          <link rel='canonical' href={status.get('url')} />
         </Helmet>
       </Column>
     );