feat: Parse newlines in JSON message as row separators.

[johnnesky]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide
• I ran npm run format and npm run lint

The details

Resolves

Fixes #6809. Interprets newline characters in the JSON message as dummies a new subclass of Input called EndRowInput that force any following inputs to be rendered on a new row.

Proposed Changes

Behavior Before Change

Newline characters from the message are preserved, but render as regular spaces by the browser in a label field.

Behavior After Change

Newline characters are converted to special dummy end-row inputs that force the next input to be rendered on a new line. (Also, these dummies use the same alignment as the implicit last dummy.)

The common RenderInfo recognizes the new dummies and handles them appropriately.

Reason for Changes

This allows more customization of block layout, including putting inline inputs on multiple rows.

Test Coverage

Unit tests in block_json_test.js and block_test.js test token parsing and conversion to dummies. Rendering is not tested.

Documentation

Information about using newline characters in JSON messages, and the new "input_end_row" JSON input type, could be added to: https://developers.google.com/blockly/guides/create-custom-blocks/define-blocks

[BeksOmega]

Generally LGTM! Mostly comments about renaming parameters :P

Wrt documentation: yes we should definitely document this. Could you file a docs issue for that (when you have time) and add it to our Q2 Github Project?

Also @maribethb the idea was that this doesn't force v10 (even though it's technically a breaking change in that it would change block rendering for people currently using \n) correct?

[BeksOmega]

Another more design-related question (possibly for @maribethb ) Have we considered adding some more generic extra options to inputs that would allow them to be rendered differently? E.g. https://github.com/google/blockly/pull/3219/files#diff-e01c94caccf98f950fdbe393516b2595473c2e1f04e9f302ec62ed66549e2886R41

I believe this would allow App Inventor to implement their indented inputs (which it seems they still want) relatively easily externally.

[Edit: Discussed this with Rachel and neither of us really like the solution of "just allow people to append extra data". So we either want to have this PR go in as-is, or we want to do some more designwork to see if there's a more structured way to support alternative rendering]

[johnnesky]

I've reimplemented this as a new subclass of Input, similar to DummyInput!

[johnnesky]

Created an issue to add documentation: #7360

[johnnesky]

Added input_end_row to the block factory demo.

[BeksOmega]

Generally LGTM! Just a few little things =)

[BeksOmega]

Nit: Update tooltip.

[johnnesky]

I updated the tooltips for both this and dummy inputs, please take a look.

[johnnesky]

Created google/blockly-samples#1854 to deprecate the renderer plugin that accomplished something similar.