fix(a11y): for "Type a comment…" dialog

[arturfrombox]

Description of Changes

• WCAG 2.0 Level A - 1.3.1 Info and Relationships - Medium Impact. Draft editor component should indicate whether it can accepts multiple lines of input, so aria-multiline="true" was added.
• WCAG 2.0 Level A - 2.1.1 Keyboard - Serious Impact. The "Type a comment…" dialog did not manage keyboard focus correctly. It should be maintaining focus within the dialog and removing focus from the rest of the page . So the tabIndex and focus traps were added. (ref. https://www.w3.org/WAI/ARIA/apg/patterns/dialog-modal/examples/dialog/)
• WCAG 2.0 Level A - 4.1.2 Success Criterion - Medium Impact. The "Type a comment…" dialog should be presented as a dialog, so the role="dialog" attribute was added. Also interactive popup button received an aria-haspopup attribute in order to indicate that dialog element can be triggered by the button.

[arturfrombox]

@jstoffan thanks for taking a look, I updated the PR