Cleanup Interop in System.Drawing.Common to follow repo guidelines

[safern]

I just submitted a PR to cleanup some of the System.Drawing.Common Interop. Having that model lead to a bug where we called a Windows PInvoke in Unix causing an exception.

I partially cleaned this up as part of the fix in: #49405

[ghost]

Tagging subscribers to this area: @safern, @tarekgh
See info in area-owners.md if you want to be subscribed.

Issue Details

---

I just submitted a PR to cleanup some of the System.Drawing.Common Interop. Having that model lead to a bug where we called a Windows PInvoke in Unix causing an exception.

I partially cleaned this up as part of the fix in: #49405

Author:	safern
Assignees:	-
Labels:	area-System.Drawing
Milestone:	-

[huoyaoyuan]

Working on it. @safern some questions related to interop:

It's targeting down level frameworks. Can function pointers be used for interop in this case?

It's using HandleRef heavily. However, HandleRef is documented to be replaced by SafeHandle. Is such a refactor required?

[safern]

It's targeting down level frameworks. Can function pointers be used for interop in this case?
It's using HandleRef heavily. However, HandleRef is documented to be replaced by SafeHandle. Is such a refactor required?

@jkotas could you help with those questions? I don't know the answer.

[jkotas]

It's targeting down level frameworks. Can function pointers be used for interop in this case?

Function pointers can be used for targets prior .NET 5 with some limitations. In particular, the unmanaged calling convention has to be always explicitly specified prior to .NET 5.

HandleRef is documented to be replaced by SafeHandle. Is such a refactor required?

No, it is not strictly required to avoid HandleRefs. The code written using SafeHandles tends to be more robust (less chance of handle leaks or use-after-free bugs).

[ViktorHofer]

Closing as dup of #51565