Test Suite Overhaul

[allthesignals]

Describe the bug
Current test suite runs locally, but doesn't run in GH CI. I've had dozens of theories why it can't run in GH CI, but I can't yet prove any of these.

I think the culprit comes down to the dependency on running a GPU hardware dependency, WebGL, in containers...

Additional context

Lots of difficulties here: #1058.

Not yet sure what an overhaul might look like. This is very hard to test. One idea is a refactor of map-related code: adding wrapper code around all interactions with ember-mapbox-gl. For code that involves visual changes, the wrapping layers should render something in the DOM. We can assert against the DOM in testing...

[allthesignals]

one way to test without as much stubbing of mapbox-gl internals is to add something that runs queryRenderedFeautures(), render those into the DOM, and assert against that output.

[allthesignals]

One possible issue causing this is huge memory leaks: https://github.com/emberjs/ember-qunit/blob/master/docs/TEST_ISOLATION_VALIDATION.md.

I notice Sinon in the stack trace.