Honour coords.z when passed to TileLayer.getTileUrl

[yohanboniface]

cf #6004 #6006

Before this change, coords.z would not taken into account, and was always overriden by this._tileZoom.
In the normal flow, coords.z is anyway set from this._tileZoom before getTileUrl is called (in GridLayer._update). But this prevents using getTileUrl out of this _update method. There are some scenarios where this is needed (see #5822), or (which is the case in uMap) when wanting to display a tile as a tilelayer preview.

[Falke-Design]

It looks like this could be working because of:

Leaflet/src/layer/tile/GridLayer.js

Line 691 in bbd2647

coords.z = this._tileZoom;

But I'm not sure if this makes maybe some problems with other plugins.

@IvanSanchez @mourner what do you think?

[yohanboniface]

It looks like this could be working because of:

Yep! We could also fallback to this._tileZoom in _getZoomForUrl, but it seems to me we should not have both, i.e. settings coords.z = this._tileZoom AND the fallback.

But I'm not sure if this makes maybe some problems with other plugins.

That could indeed be the case. Though for this to happen, it seems that a plugin should have rewritten the entire GridLayer._update, which is a huge piece of internal code, so maybe it's a feature if we discover that touching such internal code breaks some external code :p