Daniel Freedman ae4f422bf4 Add support for Form submission to FormElement subclasses
- Relies on `FormDataEvent`, which is supported by Chrome, Firefox, and Edge.
  - Safari and IE will need a polyfill
- Require `disabled` properties on FormElement subclasses
- Add `setFormData()` function to control what is added to the Form submission
- Set `checkbox` and `radio` `value`  property to `on` by default, to match native controls

Fixes #289

PiperOrigin-RevId: 385248919
2021-07-16 16:50:49 -07:00
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