WebGPURenderer: Ensure valid state in compileAsync().

[Mugen87]

Related issue: #32984

Description

As pointed out in #34481 (comment), compileAsync() does not guarantee to operate under the correct renderer state.

compileAsync() never set up the renderer state a normal render has, e.g. the internal framebuffer target, so properties like currentSamples were evaluated wrongly during pre-compilation. This can lead to runtime errors or unusable pre-compilations. The state can't simply be set once because compileAsync() yields control back to the event loop and frames rendered in the meantime are not allowed to work under this state.

The idea of this PR is to track the renderer state compileAsync() relies on. Every time the method continues it sets this state, when the method yields control to the event loop it restores it. The new methods _beginPreCompile() and _finishPreCompile() are doing this. They must be called at different locations in pairs so the state is valid.

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

	Before	After	Diff
Core	389.18 102.13	389.18 102.13	+0 B +0 B
WebGL	372.69 87.97	372.69 87.97	+0 B +0 B
WebGPU	709.07 195.28	709.71 195.5	+635 B +224 B
WebGPU Nodes	707.06 194.96	707.69 195.19	+635 B +230 B

🌳 Bundle size after tree-shaking

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

	Before	After	Diff
WebGL	516.1 124.92	516.1 124.92	+0 B +0 B
WebGPU	762.77 204.86	763.41 205.07	+635 B +215 B
WebGPU Nodes	711.43 192.13	712.07 192.34	+635 B +213 B