mergedSchema() {
    const mergedSchema = {};

    this._schemaKeys.forEach((key) => {
      const keySchema = this._schema[key];
      mergedSchema[key] = keySchema;

      keySchema.type.definitions.forEach((typeDef) => {
        if (!(SimpleSchema.isSimpleSchema(typeDef.type))) return;
        const childSchema = typeDef.type.mergedSchema();
        Object.keys(childSchema).forEach((subKey) => {
          mergedSchema[`${key}.${subKey}`] = childSchema[subKey];
        });
      });
    });

    return mergedSchema;
  }
@returns {Object} The entire schema object with subschemas merged. This is the
equivalent of what schema() returned in SimpleSchema < 2.0

Note that this returns the raw, unevaluated definition object. Use `getDefinition`
if you want the evaluated definition, where any properties that are functions
have been run to produce a result.