docs: add technical changelog for Minecraft snapshot 25w37a (#28)

Author: Neluxx

1.21.9/25w37a.md

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+pack breaking | Data pack format has been increased to `87.0`.
+
+pack breaking | Resource pack format has been increased to `69.0`.
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+debug | Some debug features that were previously removed during compilation are now preserved and can be used by players.
+
+gamerule breaking | Changed name of gamerule `enableCommandBlocks` to `commandBlocksEnabled`.
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+assets | Moved the result slot of `gui/container/villager.png` up by one pixel.
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+shader | A new `PER_FACE_LIGHTING` flag has been added to the `core/entity.vsh` and `core/entity.fsh` shaders. When set, cardinal lighting will be computed separately for front- and back-faces.
+
+shader breaking | Changed shader version from 150 to 330 for all shaders, as OpenGL 3.3 is now required.