Fix Interop.Gdi32.StartDoc p/invoke

[elinor-fung]

StartDoc takes a pointer to a DOCINFO struct. We had DOCINFO defined as a class on the managed side such that built-in marshalling would marshal it as a pointer. With the switch to custom marshalling via NativeMarshalling, we ended up marshalling the struct that is the native representation rather than a pointer to it.

This switches the DOCINFO to a struct and updates the parameter to StartDoc to be in, such that it should be marshalled as a pointer to the struct by both generated and built-in marshalling.

See #76538. This is the fix in main. We will need to backport to 7.0.

cc @ericstj @JeremyKuhne

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Issue Details

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StartDoc takes a pointer to a DOCINFO struct. We had DOCINFO defined as a class on the managed side such that built-in marshalling would marshal it as a pointer. With the switch to custom marshalling via NativeMarshalling, we ended up marshalling the struct that is the native representation rather than a pointer to it.

This switches the DOCINFO to a struct and updates the parameter to StartDoc to be in, such that it should be marshalled as a pointer to the struct by both generated and built-in marshalling.

See #76538. This is the fix in main. We will need to backport to 7.0.

cc @ericstj @JeremyKuhne

Author:	elinor-fung
Assignees:	-
Labels:	area-System.Drawing
Milestone:	-

[elinor-fung]

/backport to release/7.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3179059542

[ericstj]

LGTM, thank you @elinor-fung

[smasher164]

LGTM