fix: detect iOS in TextureFormatSelector

[kurotu]

🔍 What type of PR is this?

• 🐛 Bug fix
• ✨ New feature
• 📖 Documentation update
• 🎨 Refactoring
• 🧪 Test
• ⏪ Revert
• 📝 Other

📝 Description

Fixed the issue where uncompressed textures were compressed with PC format on iOS build target

🔗 Related Issue

No related issues.

✅ Changes

• Added iOS detection to TextureFormatSelector.ResolvePlatform().
• Added iOS to texture compressor documentation.

⚠️ Breaking Changes

• Yes, this PR contains breaking changes.
• No, this PR is fully backward-compatible.

🧪 Testing

Please describe the tests that you ran to verify your changes.

• Confirmed it works in Unity 2022.3.22f1
• Confirmed package import via VRChat Creator Companion
• Verified texture compression works correctly on test avatars
• RGBA32 textures are compressed with ASTC on iOS build target

📸 Screenshots / Videos

N/A

💌 To the Reviewers

N/A

Additional Context

N/A

[Copilot]

Pull request overview

This PR fixes a bug where iOS builds were incorrectly using Desktop (DXT/BC) texture compression formats instead of Mobile (ASTC) formats. The fix adds iOS to the platform detection logic in TextureFormatSelector.ResolvePlatform(), ensuring that iOS builds use the appropriate ASTC compression formats like Android builds already do.

Changes:

• Modified platform detection to classify iOS as a Mobile platform alongside Android
• Updated documentation to reflect iOS support in texture format descriptions

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Editor/TextureCompressor/Core/Services/TextureFormatSelector.cs	Added iOS to the BuildTarget check in ResolvePlatform() method to classify it as Mobile platform
Documentation~/avatar-compressor-docs/content/docs/components/texture-compressor.mdx	Updated English documentation to include iOS in Mobile platform references
Documentation~/avatar-compressor-docs/content/docs.ja/components/texture-compressor.mdx	Updated Japanese documentation to include iOS in Mobile platform references
CHANGELOG.md	Added entry in Unreleased section documenting the bug fix

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[Limitex]

Thank you for the contribution! I've reviewed the changes and everything looks good. Merging now.

Note: The release may be slightly delayed as I'm currently reworking the VPM package distribution system.