[FEATURE] Gray16 support

[tlm9201]

Is your feature request related to a problem?

i want to use 16bit grayscale pngs but it looks like it doesnt exist in skiasharp: https://learn.microsoft.com/en-us/dotnet/api/skiasharp.skcolortype

Describe the solution you would like

add SkColorType.Gray16

Describe alternatives you have considered

n/a

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[github-actions]

Triage Summary

No labels will be applied as the issue is a feature request for adding Gray16 support, and there are no applicable labels available.

This issue is not a regression but rather a request for new functionality in SkiaSharp related to 16-bit grayscale PNGs.

Additional remarks:

• The issue suggests the addition of SkColorType.Gray16, but there are no relevant existing labels for such feature requests, particularly in the context of backend or graphics rendering.

Detailed Summary and Actions

Summary of the triage:

• The issue is a feature request rather than a bug fix or performance issue.
• It requests support for 16-bit grayscale PNGs specifically, focusing on SkColorType.Gray16.
• There are no predefined labels for feature requests, enhancements, or related functionality in the current labeling system.

Summary of the actions that will be performed:

Action	Item	Description
No Action	N/A	The issue does not fit into any existing labeling categories, specifically for feature requests.

This entire triage process was automated by AI and mistakes may have been made. Please let us know so we can continue to improve.

[molesmoke]

There's no Gray16 support upstream:
https://api.skia.org/SkColorType_8h.html