Renderers: Add support for EAC texture formats.

[castano]

This PR adds support for EAC format as discussed in: #31695

Support for EAC formats required the following changes:

• Added new constants for the EAC formats with the corresponding GL enum values. I've added support for both signed and unsigned variants.
• Since the format constants match the GL enums, the KTXLoader does not need any changes.
• The KTX2Loader is updated to handle the EAC Vulkan formats and translate them to the corresponding GL formats used by three.js internally.
• Added handling for the new formats where necessary. In particular, enable normal rg packing in NormalMapNode when the format is EAC_RG. Let me know if other parts of the code would need to be aware of these new formats.

In the future it may also be interesting to enable the use of SNORM variants as normal maps. This requires changes to the NormalMapNode to avoid unpacking from UNORM to SNORM. However, the use of SNORM textures is fairly rare, so this will be proposed as a separate PR.

This contribution is funded by Ludicon

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	356.57 86.51	356.97 86.61	+400 B +100 B
WebGPU	616.86 173.17	617.35 173.31	+498 B +139 B
WebGPU Nodes	615.46 172.92	615.96 173.06	+498 B +136 B

🌳 Bundle size after tree-shaking

Minimal build including a renderer, camera, empty scene, and dependencies.

	Before	After	Diff
WebGL	488.44 121.33	488.7 121.39	+268 B +59 B
WebGPU	689.09 189.08	689.46 189.19	+368 B +110 B
WebGPU Nodes	630.5 172.27	630.87 172.37	+368 B +99 B