[Cashtab] Add op return raw field to send xec screen

Summary:
T3460

Add support for op_return_raw input to Cashtab's SendXec UI.

Currently, this can be set by bip21. However, it is confusing and scary when it is set this way, because there is no parsing of the op_return_raw string -- so the user does not know what the tx is.

Add parsing and render a preview window of the parsed op_return_raw. Support all protocols known to Cashtab.

Instead of the kind of useless "bip 21 alert" divs -- we now just configure the form the way a user would do manually and disable the inputs.

The "webapp tx request" is preserved, for now. Will clean this up in a separate diff.

Test Plan:
npm test

This is live at https://cashtab-local-dev.netlify.app/

Test with extension

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15874