feat!: add block definition to multiline text field plugin (#2202)

* chore: force-install blockly 10.4.0-beta.1 for development

* feat: add text_multiline block and associated generators

* feat: update test page to use new block and field

* feat: README

* chore: respond to PR feedback

BREAKING CHANGE: The multiline text input field no longer registers itself on load. The developer must either manually register the field or install blocks, which will install the field. This is part of a move to have no side effects in field and block definitions, so that tree-shaking can remove unwanted fields and blocks.

plugins/field-multilineinput/README.md

@@ -1,6 +1,6 @@
 # @blockly/field-multilineinput [![Built on Blockly](https://tinyurl.com/built-on-blockly)](https://github.com/google/blockly)
 
-A [Blockly](https://www.npmjs.com/package/blockly) multilineinput field.
+A [Blockly](https://www.npmjs.com/package/blockly) multilineinput field and associated block.
 
 ## Installation
 
@@ -18,6 +18,8 @@ npm install @blockly/field-multilineinput --save
 
 ## Usage
 
+### Field
+
 This field accepts up to 3 parameters:
 
 - "text" to specify the default text. Defaults to `""`.
@@ -28,12 +30,18 @@ This field accepts up to 3 parameters:
 
 The multiline input field is a subclass of Blockly.FieldInput
 
+If you want to use only the field, you must register it with Blockly. You can
+do this by calling `registerFieldMultilineInput` before instantiating your
+blocks. If another field is registered under the same name, this field will
+overwrite it.
+
 ### JavaScript
 
 ```js
 import * as Blockly from 'blockly';
-import {FieldMultilineInput} from '@blockly/field-multilineinput';
+import {registerFieldMultilineInput} from '@blockly/field-multilineinput';
 
+registerFieldMultilineInput();
 Blockly.Blocks['test_field_multilineinput'] = {
   init: function () {
     this.appendDummyInput()
@@ -50,8 +58,9 @@ Blockly.Blocks['test_field_multilineinput'] = {
 
 ```js
 import * as Blockly from 'blockly';
-import '@blockly/field-multilineinput';
+import {registerFieldMultilineInput} from '@blockly/field-multilineinput';
 
+registerFieldMultilineInput();
 Blockly.defineBlocksWithJsonArray([
     {
         "type": "test_field_multilineinput",
@@ -65,6 +74,36 @@ Blockly.defineBlocksWithJsonArray([
     }]);
 ```
 
+### Blocks
+
+This package also provides a simple block containing a multiline input
+field. It has generators in JavaScript, Python, PHP, Lua, and Dart.
+
+You can install the block by calling `textMultiline.installBlock()`.
+This will install the block and all of its dependencies, including the
+multiline input field. When calling `installBlock` you can supply one or
+more `CodeGenerator` instances (e.g. `javascriptGenerator`), and the install
+function will also install the correct generator function for the
+corresponding language(s).
+
+```js
+import {javascriptGenerator} from 'blockly/javascript';
+import {dartGenerator} from 'blockly/dart';
+import {phpGenerator} from 'blockly/php';
+import {pythonGenerator} from 'blockly/python';
+import {luaGenerator} from 'blockly/lua';
+import {textMultiline} from '@blockly/field-multilineinput';
+
+// Installs the block, the field, and all of the language generators.
+textMultiline.installBlock({
+  javascript: javascriptGenerator,
+  dart: dartGenerator,
+  lua: luaGenerator,
+  python: pythonGenerator,
+  php: phpGenerator,
+});
+```
+
 ### API reference
 
 - `setMaxLines`: Sets the maximum number of displayed lines before