Remove JSON generation step in key

[sjg-wdw]

To generate a layoutKey when parsing geometry for a tile, the toolkit constructs JSON to use, presumably in the comparison.

https://github.com/maplibre/maplibre-gl-native/blob/0058c3307285c4116270848de9b4c8d182a2c345/src/mbgl/tile/geometry_tile_worker.cpp#L354
https://github.com/maplibre/maplibre-gl-native/blob/main/src/mbgl/renderer/group_by_layout.cpp

Very inefficient, requires a JSON writer for no good reason and is slow.
Looks like Javascript thinking to me. Should be replaced with a sort key from the structure itself.

[louwers]

@sjg-wdw Would you like to try to put a bounty on this, in the hope that someone from outside the Metal team picks it up?

[sjg-wdw]

That's a great idea! @mwilsnd might want to chime in with some more detail.

[louwers]

For someone that wants to pick this up, the bounty applies to making a design proposal / plan to fix this, not the implementation itself.