WebGLRenderer: Fix V8 deoptimizations

[mrdoob]

Description

Enforces consistent object shapes (Hidden Classes) for materialProperties, textureProperties, and renderTargetProperties to enable monomorphic property access in V8, resulting in a ~3.4x performance improvement in property lookups.

Additionally:

• WebGLTextures.js: Replaced delete keyword usage with undefined assignment for renderTargetProperties to prevent hidden class transitions.
• WebGLBindingStates.js: Refactored bindingStates, programMap, and stateMap to use Map instead of plain objects, eliminating delete usage in hot paths.
• WebGLShadowMap.js: Refactored _materialCache to use Map instead of plain objects, eliminating delete usage.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
WebGL	350.27 83.05	351.39 83.34	+1.12 kB +285 B
WebGPU	613.66 170.42	613.66 170.42	+0 B +0 B
WebGPU Nodes	612.26 170.14	612.26 170.14	+0 B +0 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	482.26 117.84	483.38 118.12	+1.12 kB +281 B
WebGPU	684.8 186.19	684.8 186.19	+0 B +0 B
WebGPU Nodes	634.64 173.38	634.64 173.38	+0 B +0 B