feat: add block to use WP Rainbow login outside of login screen gh-8

[x] Pull login component out of login.jsx and make it reusable
[x] Move siteLoginText to utilities file
[x] Check how login looks when WP.com also enabled (moving to new ticket)
[x] Confirm multiple blocks can be added to page (no shared state though, maybe followup?)
[x] Try using default RainbowKit button style for block (doesn't work well, going to mimic button block instead)
[x] Try moving siteLoginText include to the login page implementation
[x] Add docs for mockLogin prop
[x] Figure out a way to make the button text editable
[x] Add option to block to change redirect URL
[x] Figure out what's going on with editorScript, editorStyle, and style
[x] Conditionally enqueue scripts on frontend if block is used

davisshaver / wp-rainbow