Make PlatformConfiguration properties trimmable (fixes tvOS compilation)

[maxkatz6]

Description of Change

Previously SkiaSharp used old APIs to conditionally execute platform specific APIs. Specifically, RuntimeInformation.IsOSPlatform is known to be non-trimmable.

It caused some Windows PInvokes to be included in the non-windows binaries. For most platform it didn't really cause any problems, but apparently tvOS linker is more sensitive (see #2715)

This PR changes PlatformConfiguration class:

1. Use newer trimmer friendly OperatingSystem.IsWindows() method instead of non-trimmable RuntimeInformation.IsOSPlatform (OSPlatform.Windows).
2. Remove static ctor, and instead move these checks to the property getters.

On .NET6+ targets with trimmer enabled these calls will be eliminated and values will be inlined.

Non trimmed SkiaSharp:

Trimmed SkiaSharp with "-r tvos-arm64" (hint for the compiler to replace OperatingSystem.IsWindows with "false").
As we can see, windows specific class is completely removed as unused.

Bugs Fixed

• Fixes [BUG] Publishing tvOS application with SkiaSharp fails #2715

API Changes

None.

Behavioral Changes

None.

Required skia PR

None.

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Merged related skia PRs
• Changes adhere to coding standard
• Updated documentation

This PR should also be backportable with no conflicts.

[maxkatz6]

Alternatively, we can add more preprocessor conditional checks for each target, eliminating code blocks during per specific target framework. In this way SkiaSharp for "net7.0-tvos" would never include windows code to begin with.
Though, it's probably unnecessary. Also, it would complexity.

[maxkatz6]

@mattleibow hi! How does this PR look? CI build failing seems to be unrelated.

[mattleibow]

Retrying thre build. Sometimes the tests explode for no reason.

[mattleibow]

The macos tests are still crashing... I have retried 5 times and a fail already retries by default...

[maxkatz6]

@mattleibow that's weird, as with .NET 6+, RuntimeInformation API should simply redirect to OperatingSystem API, making them equivalent (except of trimming capabilities): https://github.com/dotnet/runtime/blob/v6.0.26/src/libraries/System.Runtime.InteropServices.RuntimeInformation/src/System/Runtime/InteropServices/RuntimeInformation/RuntimeInformation.cs#L52

CI worker only when I tried to revert my changed... I wonder if it's just a consistent fluke or some hidden detail behind CI infra here.
Trying to see if it works with OperatingSystem.IsWindows () only, without changing behavior for other platforms.

[mattleibow]

I see some other PRs are crashing on macOS... I wonder if some of my GC tests are crashing on a newer .net service release. But this is green now, so I am thinking this is intermittant... It can't be the check is crashing the test runner...

[maxkatz6]

@mattleibow okay. Let me know if any changes are required from my side. I can rebase this PR back to the state where OperatingSystem was used on every platform, not only Windows.

[mattleibow]

Maybe do that, let's make this code right and I will continue to investigate why CI is crashing. It looks also to just be the public bot.

[maxkatz6]

@mattleibow done