[Suggestion] Improve the docs for mixins

[canonic-epicure]

The official documentation contains very old docs for mixins: https://www.typescriptlang.org/docs/handbook/mixins.html

Since then, the mixin pattern has evolved:
https://mariusschulz.com/blog/typescript-2-2-mixin-classes
https://www.bryntum.com/blog/the-mixin-pattern-in-typescript-all-you-need-to-know/

I'm volunteering to update documentation with the "officially blessed" content from the 2 links above.

The problem with the approach from the handbook, is that it uses ad-hoc copying of properties from one prototype to another and mixins will not compose well, because one can't use super in methods. Such copying also feels not type-safe. The new approach is free from these drawbacks.

If someone can point me to the canonical source of the mixins docs page (source file in some repo or a wiki page?) I'm volunteering to update the docs with the "modern" mixin pattern.

[elibarzilay]

(See also the examples that @orta added recently...)

[typescript-bot]

Hello! As per #2804, we are automatically closing all open issues. Please see #2804 for a description of what issues and PRs can be accepted going forward.