@blockly/plugin

import * as Blockly from 'blockly';
import {FieldTemplate} from '@blockly/plugin';
Blockly.Blocks["test_field_template"] = {
  init: function () {
    this.appendDummyInput()
      .appendField("template: ")
      .appendField(new FieldTemplate(...), "FIELDNAME")
  }
};

import * as Blockly from 'blockly';
import '@blockly/plugin';
Blockly.defineBlocksWithJsonArray([
    {
        "type": "test_field_template",
        "message0": "template: %1",
        "args0": [
            {
                "type": "field_template",
                "name": "FIELDNAME",
                "value": ...
            }
        ]
    }]);