Remove types deriving from JsonTypeInfo<T> and mark as sealed.

[eiriktsarpalis]

Removes a number of generic types deriving from JsonTypeInfo<T> and marks the type itself as sealed. It also removes a number of abstract and virtual methods that were being used to perform delayed metadata resolution. The type itself should now only contain data and caches, with any metadata resolution logic being moved out to static factory methods.

Contributes to #80917.

cc @eerhardt

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[ghost]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Removes a number of generic types deriving from JsonTypeInfo<T> and marks the type itself as sealed. It also removes a number of abstract and virtual methods that were being used to perform delayed metadata resolution. The type itself should now only contain data and caches, with any metadata resolution logic being moved out to static factory methods.

Contributes to #80917.

cc @eerhardt

Author:	eiriktsarpalis
Assignees:	-
Labels:	area-System.Text.Json, new-api-needs-documentation
Milestone:	-

[ghost]

Tagging subscribers to 'size-reduction': @eerhardt, @SamMonoRT, @marek-safar
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Removes a number of generic types deriving from JsonTypeInfo<T> and marks the type itself as sealed. It also removes a number of abstract and virtual methods that were being used to perform delayed metadata resolution. The type itself should now only contain data and caches, with any metadata resolution logic being moved out to static factory methods.

Contributes to #80917.

cc @eerhardt

Author:	eiriktsarpalis
Assignees:	eiriktsarpalis
Labels:	area-System.Text.Json, new-api-needs-documentation, size-reduction
Milestone:	-