Refactor loginRequired.js with Aphrodite and commonForm

[luixxiul]

Test plan

#8011 (comment)

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Describe the issue you encountered: Refactor loginRequired.js with Aphrodite, applying .commonForm (which shall be implemented with PR #7995) instead of .genericForm

Currently there are only three other instances where .genericForm is applied (autofillAddressPanel.js, autofillCreditCardPanel.js, and addEditBookmarkHanger.js), and in every case styles which genericForm defines are overwritten by what commonForm is going to do so (title color, padding inside the dialog, etc). Keeping both of them is a cause of style inconsistency.

• Any related issues: Create commonForm with Aphrodite #7990 Updated style for importBrowserDataPanel.js #7996 Discard .genericForm and .commonForm from forms.less #8010