Feat: support specular intensity and F0 color in dielectric material

[zhuxudong]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature.

What is the current behavior? (You can also link to an open issue here)

KHR_materials_specular is not supported and F0 & F90 can't be modified in dielectric material.

What is the new behavior (if this is a feature change)?

Supported.

Other information:

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 16.18497% with 145 lines in your changes missing coverage. Please review.

Project coverage is 43.83%. Comparing base (aca8331) to head (4b0cd6a).
Report is 1801 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/core/src/material/PBRBaseMaterial.ts	17.80%	60 Missing ⚠️
packages/core/src/material/PBRMaterial.ts	14.28%	24 Missing ⚠️
...der/src/gltf/extensions/KHR_materials_clearcoat.ts	0.00%	17 Missing ⚠️
.../loader/src/gltf/extensions/KHR_materials_sheen.ts	0.00%	16 Missing ⚠️
...ader/src/gltf/extensions/KHR_materials_specular.ts	0.00%	15 Missing ⚠️
...es/loader/src/gltf/extensions/KHR_materials_ior.ts	0.00%	7 Missing ⚠️
packages/loader/src/gltf/parser/MaterialParser.ts	58.33%	5 Missing ⚠️
.../extensions/KHR_materials_pbrSpecularGlossiness.ts	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #697      +/-   ##
==========================================
- Coverage   48.09%   43.83%   -4.27%     
==========================================
  Files         349      410      +61     
  Lines       18979    21605    +2626     
  Branches     2547     2991     +444     
==========================================
+ Hits         9128     9470     +342     
- Misses       9851    12135    +2284     

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