Improve performance of Heightmap Debug Renderer

I would like to suggest improving the performance impact of the heightmap debug renderer on Java Edition. At present, it has a severe performance issue when it is enabled, as the current version of the code is creating performance bottlenecks (https://bugs.mojang.com/browse/MC/issues/MC-311099).

Earlier this year, I submitted a bug report with proof that the heightmap debug renderer worked much better before it was officially added to the debug options/properties. When I explained the situation, the bug report was closed by the developers as "not a bug" simply because part of the proof was from before a way to enable the heightmap debug renderer was added to the base game (I created a patch which allowed it to be enabled in earlier versions). However, I highly doubt that performance bottlenecks with a debug renderer are intentional.

Thus, I would like to suggest optimising the code for it and fixing the bottlenecks. If Mojang wants the heightmap debug renderer to be useful to the community, these performance issues need to be addressed.