Fix Linux SkiaSharp native asset version mismatch

[wieslawsoltes]

Summary

• add SkiaSharp.NativeAssets.Linux 4.148.0 to Svg.Controls.Skia.Avalonia
• keep the standalone Svg.Skia package native-neutral, preserving the application choice between SkiaSharp.NativeAssets.Linux and SkiaSharp.NativeAssets.Linux.NoDependencies
• verify packed NuGet dependency metadata and a clean linux-x64 consumer publish in build and release workflows

Root cause

Svg.Controls.Skia.Avalonia 12.0.0.14 upgraded Svg.Skia to 5.2.0 and managed SkiaSharp to 4.148.0. The SkiaSharp meta-package supplies Windows and macOS native assets, but not Linux. Avalonia.Skia therefore remained the only source of SkiaSharp.NativeAssets.Linux, at 3.119.4. On Linux, managed 4.148.0 rejected native 3.119.4 during SkiaApi initialization.

The Linux native dependency was deliberately removed from the core package in #408 after #406 so standalone consumers could choose the standard native package or the NoDependencies variant. This change retains that policy and scopes the matching standard native asset to the Avalonia controls package, whose Avalonia dependency already selects the standard variant.

Regression coverage

The new package verifier:

• rejects a direct Linux SkiaSharp native dependency in Svg.Skia
• requires Svg.Controls.Skia.Avalonia to declare the same native version as the core managed SkiaSharp dependency
• restores and publishes a clean linux-x64 consumer from the packed controls package
• verifies the resolved 4.148.0 package graph and published libSkiaSharp.so

Validation

• dotnet format Svg.Skia.slnx --no-restore
• dotnet build Svg.Skia.slnx -c Release --no-restore
• dotnet test Svg.Skia.slnx -c Release --no-build --no-restore — 3,115 passed, 40 skipped
• packed consumer verification — SkiaSharp 4.148.0 managed/native match

Fixes #554