Replace click listeners on submit buttons with submit listeners on forms

[lukaw3d]

Related to #1037 (review)

Although accessibility is good in both cases (both trigger submit on Enter and on click), only <Form onSubmit handles validation. Fix it upstream or add types+lint to enforce correct usage.

Before:

<Form>
  <Button type="submit" onClick={onSubmit}>

After:

<Form onSubmit={onSubmit}>
  <Button type="submit">

[alexander-elgin]

@lukaw3d please, can you assign the issue to me? I submitted a PR fixing it

[lukaw3d]

Sure!
I'll keep the issue open for the "Fix it upstream or add types+lint to enforce correct usage" part