Collapse attribution behind a control

[Malvoz]

There are usability issues with the attribution (some of which are mostly apparent on small screens/in small sized maps).

Problems

Here's a default size map with added opacity to the attribution container to demonstrate:

1. Controls may be hidden behind the attribution (means we fail SC 2.4.7 Focus Visible):
   
   
   

2. There are no constraints on the element containing the attribution links, which may result in the following depending on the amount of layer sources and/or the map element's size:
   
   
   

3. Sensory overload

   • Visual
   • Auditory (screen readers announce everything in the attribution on page load because it is visible)

4. Each attribution link adds to the amount of Tab key presses required to sequentially navigate past the map.

Potential solution

Collapse attribution behind a control, like MapBox does:

Collapsing attribution may have several benefits:

• There's no visible Layout Shift (so does not contribute to the Cumulative Layout Shift) when populating the attribution container with attributions after fetching layer sources.
  
  

• Improves Perceived Performance.

• Mitigates sensory overload for some users.

• Less Tab key presses required to sequentially navigate past the map.

[prushforth]

FWIW, the widget is supposed to de-dupe the attribution, so in the case of many layers from the same source, only one attribution entry should be created. This may not work, but that's the theory.

[Malvoz]

widget is supposed to de-dupe the attribution

That is probably the case, I simply modified the DOM in devtools to present the potential issue (with having multiple different sources).

[prushforth]

How persnickety would Web Platform Tests be about the UI to the attribution control? I like the approach MapBox takes, but some browsers might like to be more explicit.

[AliyanH]

implemented in #815