implemented TMS in terms of UrlTemplateImageryProvider

[sen-lu]

due to its async nature, the benefits of implementing TileMapServiceImageryProvider in terms of UrlTemplateImageryProvider as it currently stands are limited
@pjcozzi it might be more complicated than just creating setter functions for the properties in UrlTemplateImageryProvider, since the fileExtension property pulls data from the promise but is also necessary to create the template url for UrlTemplateImageryProvider

[pjcozzi]

@kring do you have a minute to look at this and advise?

[kring]

Yeah there's not a ton of benefit here, because TMS URLs are so simple to build, and that's the only part that UrlTemplateImageryProvider really helps with. But the code here can be simplified a bit more, making it shorter, more reliable, and faster than the current implementation, at least a little.

To make this simpler, don't set a bunch of fields on TileMapServiceImageryProvider and then call a parameterless buildImageryProvider. Just construct the UrlTemplateImageryProvider directly from local variables in the two places. You should be able to get rid of all the error event, credit, and ready handling.

[pjcozzi]

Part of #2814.

[pjcozzi]

@kring thanks for the review.

[sen-lu]

I'm opening two new pull requests on two renamed branches, one for TileMapServiceImageryProvider (directly addressing the comments here) [#3150] and one for related test fixes [#3151]