Add support {-y} for TileLayer

[ShivangMishra]

modified TileLayer::getTileURL to support {-y} syntax from within infinite coordinate systems.
The change is safe - the only new behavior is supporting {-y} in some cases which previously were unsupported.

Fixes: #8395

[Falke-Design]

I didn't checked the code but a test is needed anyway

[ShivangMishra]

@Falke-Design I need to add a test ?

[Falke-Design]

For some reason there was a expliciet test for {-y} to be not set on infinite crs (this is also then one who is failing):

Leaflet/spec/suites/layer/tile/TileLayerSpec.js

Lines 327 to 345 in c33a57c

	it('Does not replace {-y} on map with infinite CRS', function () {
	var simplediv = document.createElement('div');
	simplediv.style.width = '400px';
	simplediv.style.height = '400px';
	simplediv.style.visibility = 'hidden';
	document.body.appendChild(simplediv);
	var simpleMap = L.map(simplediv, {
	crs: L.CRS.Simple
	}).setView([0, 0], 5);
	var layer = L.tileLayer('http://example.com/{z}/{-y}/{x}.png');
	expect(function () {
	layer.addTo(simpleMap);
	}).to.throwError('No value provided for variable {-y}');
	simpleMap.remove();
	document.body.removeChild(simplediv);
	});

Added with: #4338

[ShivangMishra]

@Falke-Design This is what I understood -
In the issue #4338 , the problem was that TMS "needs an upper bound for the CRS's Y coordinate, to be able to flip the tile row". In the case of infinite crs, we don't have an upper bound, that's probably why they added the check on {-y}.
In our case, we don't use the upper bound, we simply set {-y} = (-1 * coords.y) - 1.
So, I think the test should be fixed. Do you have any suggestions for me regarding #8575 ?

[Falke-Design]

@mourner @IvanSanchez maybe you can take a look into this. The tile and rendering logic is still pretty hard for me

[ShivangMishra]

@Falke-Design I reforked this repo. Should I open a new PR for this issue #8395 ?

[Falke-Design]

@ShivangMishra go for it