Invoke PrintDialog.ShowDialog() does not show Print dialog successfully

• .NET Core Version: .NET Core SDK 5.0.100-preview.1.20106.1 + the VSIX Inserted into Dev16 16.5.0 [29803.141.master]

• Have you experienced this same bug with .NET Framework?: No

Problem description:
Invoke PrintDialog.ShowDialog() does not show Print dialog successfully.

More Info:

1. This is a regression issue, it's not reproducing when targeting .NET Core 3.1.
2. This issue also cannot reproduce with Framework project.

Actual behavior:
No expected Print dialog shown.
.NET Core 5.0 screenshot:

Expected behavior:
The Print dialog should be shown successfully.
.NET Core 3.1 screenshot:

Minimal repro:

1. Create a Winforms Core application.
2. Drag and drop a button to the form.
3. Double click the button1 to generate the button1_click event, then add following code to it:
   PrintDialog pdlg = new PrintDialog();
   pdlg.ShowDialog();
4. Build and run.
5. Click the button1 to see whether the Print dialog is popping up.
   PrintDialogIssue.zip

[RussKie]

I haven't bisected, but looking at the history we probably disturbed it in #2594.
Guessing these classes, having one of the fields modified, caused some misalignment, and caused the call to UnsafeNativeMethods.PrintDlg(data) fail.

/cc: @gpetrou

[weltkante]

@RussKie the PR you linked moved the int m_Flags; field which broke the binary layout. I'm adding comments to the PR to highlight the mistakes.

[RussKie]

Thank you @weltkante 👍 somehow I failed to see it myself