Add tests for distance expression

[zmiao]

Gl-native implementation: mapbox/mapbox-gl-native#16397

[asheemmamoowala]

@zmiao Some of the render tests use large image file sizes or have more complex data sets than looks to be necessary. Can these be simplified or reduced in size? Reduced test cases make debugging easier when something breaks.

[asheemmamoowala]

@zmiao This is quite a large size for a render test. Would it be possible to make a smaller test image?

[zmiao]

The intention of this test case is to simulate a real world route and to see if it works. That's why the image size is very big, but I will try to decrease the zoom level and minimize the size.

[chloekraw]

Thanks for the context @zmiao. If it's OK to have one larger size image, I do think it would be valuable to have at least one render test that accurately reflects the real world route line use case.

[chloekraw]

@zmiao I've audited the render tests that are present. I noticed a few issues:

1. I don't think that we have any render tests with Polygon as the evaluated feature. Is this sufficiently covered by the MultiPolygon cases? Same question for Point, where we only have one render test with it as the evaluated feature.

2. We do not have render test coverage for every combination of geometry as both the input and evaluated feature. For example, there is a test for LineString as the evaluated feature with MultiLineString as input but not for MultiLineString as the evaluated feature with LineString as the input, even though the latter is also a valid implementation of distance.

3. Is there any way to add multiple geometry types as inputs or evaluated features to a single render test? The above example could be solved by adding a LineString input to the lines-to-lines distance test, for example. If we take this approach, we should come up with a different naming schema for the folders.

4. The current naming schema is not consistently applied. Some of them are "input-to-evaluatedfeature distance" while others are "evaluatedfeature-to-input distance". See below:

	evaluated feature	input	test
1	LineString	LineString	line-to-line distance
2	LineString	MultiLineString	line-to-lines distance
3	MultiLineString	MultiLineString	lines-to-lines distance
4	MultiPolygon	MultiLineString	lines-to-polygons distance
5	LineString	Point	point-to-line distance
6	MultiLineString	Point	point-to-lines distance
7	Point	Point	point-to-point distance
8	MultiPoint	Point	point-to-points distance
9	MultiPoint	LineString	points-to-line distance
10	MultiPoint	MultiLineString	points-to-lines distance
11	MultiPoint	MultiPoint	points-to-points distance
12	MultiPolygon	MultiPoint	points-to-polygons distance
13	MultiPolygon	Polygon	polygon-to-polygons distance
14	MultiPolygon	MultiPolygon	polygons-to-polygons distance

cc @alexshalamov

[chloekraw]

I think there's an extra set of close brackets here that is causing problems with this file

[zmiao]

@chloekraw Thank you very much for the thorough review and creating such a clear table! I agree that the tests are insufficient, in order to prove the equivalent evaluation result between the feature and input data, more test cases need to be added. I am working on it!