Use Metal-only Skia features on macOS and iOS

[nicoburns]

Summary

Remove skia-safe/gl on macOS and iOS, where SkiaWindowRenderer uses Metal. Explicitly enable ganesh alongside metal: gl previously enabled Ganesh transitively. Other platforms retain GL.

Keep Skia's defaults for binary-cache compatibility, removing the redundant explicit pdf selection. Surveyed all 152 published rust-skia 0.153.3 archives: every archive includes PDF/JPEG. Apple has a minimal Ganesh + Metal archive without GL/textlayout; Linux already uses the smallest GL and GL + Vulkan combinations. Windows GL-only can omit textlayout, but GL + Vulkan still requires it, so Windows remains unchanged.

Full prebuilt feature survey

Validation: formatting, Linux default check/strict Clippy, and all-feature test build pass (the crate has no tests). Resolved features match published archives for all nine desktop/Apple targets and four Linux/Windows Vulkan configurations. Strict all-feature Clippy fails on existing unused Vulkan code/argument-count lints, reproduced on main.

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/06a8de9fb4f34694b6a757de3cc36e6c
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/06a8de9fb4f34694b6a757de3cc36e6c?variant=devin-insiders
Requested by: @nicoburns

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access that start with 'Devin'.

• Disable automatic comment, CI, and merge conflict monitoring