Fix double-click issues in Edge and IE

[GUI]

Fixes #6740

Double-clicking on the map breaks panning in Edge and IE11. The issue is that after double-clicking, Edge & IE perform a text selection within the div, so then subsequent drag actions are trying to drag the selection instead of dragging the map. This fixes it by disabling text selection within the container.

A few additional notes:

• There are a few different ways to solve this, but it seemed like this CSS based approach was maybe the simplest. However, it's worth noting that user-select is only a working draft standard, although support seems pretty universal as long as vendor prefixes are used.
• I looked at adding a test for this (to ensure there's no selection after double-clicking), but I wasn't quite sure how to go about that. The unit tests don't seem to have support for checking window.getSelection, and the integration tests seem focused on style things.
• Adding this CSS to either mapboxgl-canvas-container or .mapboxgl-canvas-container .mapboxgl-canvas seems to work, so not sure if one or the other might be more appropriate. In either case, text selection still seems to work for other things, like controls or popups, since those are outside the canvas container.
• Perhaps unrelated, but the place I added it also has a CSS selector for .mapboxgl-ctrl-nav-compass, which as far as I can tell isn't used at all in the app (only .mapboxgl-ctrl-compass seems to be used). So I'm not sure if that should be removed or cleaned up (happy to open a separate PR if so).

Thanks!

Launch Checklist

• briefly describe the changes in this PR
• write tests for all new functionality
• document any changes to public APIs
• post benchmark scores
• manually test the debug page
• tagged @mapbox/studio and/or @mapbox/maps-design if this PR includes style spec changes

[jfirebaugh]

Awesome, looks great! I tagged on a fix for the compass control selector.