Replace wkid/w/s/n/e in WMS URL templates

[1ec5]

Added support for {wkid}, {w}, {s}, {n}, and {e} tokens in WMS-style background imagery templates, as described in this JOSM documentation.

The {wkid} token is particularly handy for exportImage endpoints in ArcGIS ImageServer services. (In fact, it appears multiple times, whereas the previous code only replaced each token once.) Currently, osmlab/editor-layer-index#611 works around the lack of this token by hard-coding a projection, but JOSM can use the projection property correctly: osmlab/editor-layer-index@95680b2#r31964799. Once this PR lands, we can modify the editor layer index’s tests to accept {wkid} as an alternative to {proj}.

Thanks to @don-vip for making me aware of these additional tokens.

[1ec5]

The only other unsupported token is {header(…, …), which was requested in #4812. Apparently the Fetch API does support custom headers, but that’s different enough that it should be a separate PR. Moreover, #4812 requested Referer, which is immutable. (I’d expect that overriding the referrer would only be necessary if one is using an endpoint without permission.)

[bhousel]

The only other unsupported token is {header(…, …), which was requested in #4812. Apparently the Fetch API does support custom headers, but that’s different enough that it should be a separate PR. Moreover, #4812 requested Referer, which is immutable. (I’d expect that overriding the referrer would only be necessary if one is using an endpoint without permission.)

The problem here is that we don't request the imagery via XHR or Fetch - the browser requests the imagery when we create <img> tags.

[1ec5]

Ah, good point. 😅 So in other words, this PR gets us to parity with JOSM to the extent possible.