Material: Add missing blending factors.

[Mugen87]

Fixed #23741.

Description

This PR adds the following missing blend factors:

THREE.ConstantColorFactor
THREE.OneMinusConstantColorFactor
THREE.ConstantAlphaFactor
THREE.OneMinusConstantAlphaFactor

It also adds Material.blendColor and Material.blendAlpha to make the constant blend color configurable.

The PR is implement based on the following proposal: #23754 (comment)

[github-actions]

📦 Bundle size

Full ESM build, minified and gzipped.

Filesize dev	Filesize PR	Diff
650.2 kB (161.2 kB)	651 kB (161.3 kB)	+811 B

🌳 Bundle size after tree-shaking

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

Filesize dev	Filesize PR	Diff
443.1 kB (107.2 kB)	443.7 kB (107.3 kB)	+528 B

[LeviPesin]

Should we now replace WebGPURenderer's GPUBlendFactor with these new core constants, now that all of them are supported? (I actually prefer more the WebGPUConstants' approach of defining these factors and etc in an object instead of just bunch of variables) /ping @sunag

[Mugen87]

I think it's okay of keeping them for now. Besides, this is a general topic and not specific to blending factors.