Support @deprecated, @alpha, and @beta TSDoc modifiers

[alexkreidler]

#547 mentions that a goal of future TypeDoc versions is to be compliant with TSDoc.

@deprecated is a core TSDoc standard that is used by many tools, including IDEs like VSCode to indicate deprecation.

Although @alpha and @beta are "discretionary" modifiers, they are used by API Extractor and many Microsoft APIs (e.g. rush, heft, etc), and I believe are quite useful.

I propose we either add a strikethough, "gray out" the name, or add an icon next to items that are marked deprecated.
I also propose we add icons/tags in the UI next to items that are marked @alpha and @beta.

These are likely less important than other core TSDoc features like @linking, etc, so it may likely be implemented later.

Thanks for an awesome tool!

[Gerrit0]

Definitely planned - but probably won't happen this year... I'm planning on starting on TSDoc support come January though :)

[doberkofler]

Support for @deprecated would be most appreciated

[kamranayub]

Here is a commit you could reference where we support @obsolete (before deprecated was a thing), maybe for Hacktoberfest I could add this for @deprecated

excaliburjs/typedoc-default-themes@8c824b8