"Extract base class" and "Pull member up" drop `partial` modifier from events

[jhinder]

Version Used: VS 18.0.0 Insiders

Steps to Reproduce:
On the class definition, open the lightbulb menu, select "Extract base class". In the dialog, select all members and confirm.

partial class C
{
    public partial void M();
    public partial void M() { }

    public partial int P { get; }
    public partial int P => 0;

    public partial event EventHandler E;
    public partial event EventHandler E { add { } remove { } }
}

Expected Behavior:
All members retain their partial modifiers.

Actual Behavior:
The method and the property retain their partial modifier, the event loses it.

internal class CBase
{
    public partial int P { get; }

    public event EventHandler E;

    public partial void M();
}

The same behaviour happens when there already is a base class and you select "Pull (symbol) up" on it.