Adding the Insert/Collapsible container options

[imhamad]

Greetings 👋,

We've used Lexical in our NextJS/React project, however, we've introduced all the options mentioned here: https://codesandbox.io/s/lexical-rich-text-example-5tncvy,

Now we can't introduce

1. Insert (Horizontal Line)
2. Collapsible Container 
3. Figma Document

Could anyone please shed light with some helpful resources for us to cross that bridge,

Cheers!