Remove potential leaks when type providers are misauthored

[cartermp]

(copied and paraphrased over from @dsyme's PR)

The following mistakes in type provider authoring can result in a memory leak:

1. If TP instances have mistakenly kept themselves alive by F# compiler not disposing them correctly
2. If a TP registers itself in global state, e.g. in a callback in a file watch timer or stores itself in global state in its own .dll
3. if a TP saves one of its generated ProvidedTypeDefinition in a global cache in its own .dll

The compiler should be able to still release these resources.

[smoothdeveloper]

Not too familiar with TP implementation, but it seems that the anti pattern here is storing reference to the TP instance, and maybe this extends to some other objects generated there.

Should this issue be tracked in https://github.com/fsprojects/FSharp.TypeProviders.SDK?

It maybe the guidelines in documentation and samples that would benefit from adding emphasis regarding potential memory leak if not following some rules.

[cartermp]

Fixed in #6394