fix(ui5-button): announce accessible name

[unazko]

Issue:

• The badge wasn't announced at all when an accessible-name attribute is provided
  for the ui5-button. The reason behind this behaviour is that the screen reader doesn't
  read the inner text nodes of the root button node when the same has aria-label attribute.

Solution:

• The proper badge description text is placed into the aria-label attribute of the root
  button element. As a result the screen reader won't rely on the inner text content
  for the announcements.
• Additionally the design description is also moved into the aria-label attribute,
  in order to keep a proper announcement order.

Fixes: #11350