Component fails axe tests due to role="presentation" on button element

[web-padawan]

Mentioned in #96 but is a separate problem, so I decided to extract from there.

Rule: aria-allowed-role
Impact: minor
ARIA role must be appropriate for the element (https://dequeuniversity.com/rules/axe/3.4/aria-allowed-role?application=axeAPI)

Issue target: vaadin-drawer-toggle,button
Context: <button type="button" role="presentation" tabindex="0"></button>
Fix any of the following:
  ARIA role presentation  is not allowed for given element

We tested Material Web Components demos and they don't use the role="button" on the host element. Need to test if that would work for us too.

[web-padawan]

Here is the current list of allowed elements that can use presentation role according to axe.

[web-padawan]

See https://www.w3.org/TR/using-aria/#4thrule

[anezthes]

I tested the following HTML structure with great success in Chrome and Safari using VoiceOver:

<button>
  <span part="prefix"><slot name="prefix"></slot></span>
  <span><slot></slot></span>
  <span part="suffix"><slot name="suffix"></slot></span>
</button>

[rolfsmeds]

This seems to cause some screen readers to announce button labels twice or not at all.

[rolfsmeds]

Closing in favor of https://github.com/vaadin/vaadin-button/issues/96