RFC: Improving plugin developer experience

[Gerrit0]

While TypeDoc technically supports plugins, it isn't very friendly right now to develop a plugin for... even ignoring the lack of documentation. What would be helpful when developing plugins? Lets make a list.

• Export all necessary items from the main entry point. Plugins should never need to import from typedoc/dist/....
• Transformer API - It would be really useful to have something like TS has for rewriting types rather than implementing logic to iterate over all types in all reflections example

What else is missing?

[Gerrit0]

• Plugin need some way to modify/inject output into themes - All fields missing in type documentations when the types inherit from generic types #1377, done with hooks https://github.com/TypeStrong/typedoc/blob/master/internal-docs/custom-themes.md#hooks-v0228

[Gerrit0]

A way to replace all references pointing to some reflection/symbol with another type - ideally should be covered by 2 above.