Support removing TileMap layer at negative index

[jonathandw743]

Added ability to TileMap.remove_layer using a negative index.

[AThousandShips]

The TileMap class is deprecated, so I don't think we should add new features to it like this, if we do this should be documented as well

[KoBeWi]

This is a follow-up to #54546, so it's probably fine for consistency.

[groud]

The TileMap class is deprecated, so I don't think we should add new features to it like this, if we do this should be documented as well

I don't mind much adding it for consistency. We will probably keep the TileMap node for a little while, and I don't think adding small tweaks matter much.

My main goal in marking TileMap it as deprecated was to avoid contributors/users to implement/expect new features that would improve the TileMap node only, and that the focus will be on the TileMapLayer workflow instead. But like, if a new TileMap feature is small enough, restricted to the TileMap node, and does not need to be implemented in TileMapLayer too, I don't mind much.

[jonathandw743]

The TileMap class is deprecated, so I don't think we should add new features to it like this, if we do this should be documented as well

I didn't realise this.
Just downloaded 4.3dev6 and the TileMapLayers are way better than having to pass a layer index into every function and keep track of which index corresponds to which layer etc.

[KoBeWi]

Docs need description update here:

godot/doc/classes/TileMap.xml

Lines 324 to 329 in f4b047a

	<method name="remove_layer">
	<return type="void" />
	<param index="0" name="layer" type="int" />
	<description>
	Removes the layer at index [param layer].
	</description>

Example:

godot/doc/classes/TileMap.xml

Line 344 in f4b047a

If [param layer] is negative, the layers are accessed from the last one.

Also you need to squash commits into 1.