[v2] Generate permalink to specific JSX in REPL demo

[yhatt]

As same as Block Kit Builder, REPL demo in v2 will generate a specific permalink to edited JSX. Developer will become easy to do prototyping and sharing through jsx-slack REPL.

jsx: prefix

A generated link will have a hash prefixed with #jsx: such as #jsx:XXXXXXXXX....: The encoded string of compressed JSX data by URL-safe Base64 encoding.

<Blocks>
  <Section>
    Hello, <b>world</b>!
  </Section>
</Blocks>

For example, this JSX generates https://speee-jsx-slack.netlify.app/#jsx:eJyzccrJT84utuNSULAJTk0uyczPA7EVFDxSc3LydRRskuzK84tyUmz0k-wUQYr04aps9KF6AbQEFEU=.

bkb: prefix

By prepending extra prefix bkb: to hash, REPL demo will try to redirect into Block Kit Builder with parameters generated by the converted JSON. e.g. https://speee-jsx-slack.netlify.app/#bkb:modal

It also can use together with jsx: prefix as like https://speee-jsx-slack.netlify.app/#bkb:jsx:eJyzccrJT84utuNSULAJTk0uyczPA7EVFDxSc3LydRRskuzK84tyUmz0k-wUQYr04aps9KF6AbQEFEU=.

It's useful for replacing "Preview in Slack Block Kit Builder" buttons on the documentation. They have URLs for Block Kit Builder generated in advance, but won't reflect the change of jsx-slack so we had to update URL manually when changed behavior of components. We do no longer have to worry the updation of examples by using bkb: prefix.