Performance: Mark all classes as sealed where possible

[matthewcare]

I've noticed that there have been an increasing number of pull requests for performance based improvements.

An easy performance gain can be achieved by marking relevant classes as sealed
I won't bother explaining the benefits myself, and will instead link to this article which will do a much better job than I will. (TLDR; sealed = good).

With .NET 7 a new analyzer was added which can highlight internal classes which can be marked as sealed, so that's probably a good place to start.

Later on public classes should also be considered, however each public class that is changed will be a breaking change, and therefore not possible until (at time of writing) v13.

What are people's general thoughs on this change?

[bergmania]

Overall, I like the idea.. But you are right it is breaking changes, so we have to announce such changes in the public classes.

Seems like a good idea to introduce in the internal classes.