Fix DebuggerDisplay for serializer types

[eiriktsarpalis]

Fix #65960.

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Issue Details

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Fix #65960.

Author:	eiriktsarpalis
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[TonyValenti]

@eiriktsarpalis Can I make a suggestion?

In my own code, I create a constant that contains the debuggerdisplay,nq value and reference the constant everywhere. This keeps me from having to have the magic string everywhere.

Also, as a general rule, I've found it better to be a function rather than a property because sometimes it will wind up being serialized in weird places if it is a property.

Anyway, just a few thoughts. Do with them what you will.