checkbox: should fire click event on submit button if one exists

[Splaktar]

Bug

CodePen and steps to reproduce the issue:

CodePen Demo which demonstrates the issue: https://codepen.io/Splaktar/pen/VgVZRJ?editors=1010#0

Detailed Reproduction Steps:

1. Focus the native checkbox
2. Press enter and verify that the form was not submitted (validation text doesn't display)
3. Focus the md-checkbox
4. Press enter and see that the form was submitted (validation text displays)

Examples of the native behavior

• https://jsbin.com/matuvoj/1/edit?html,js,output
• https://jsbin.com/leforagipo/1/edit?html,js,output

What is the expected behavior?

When the ENTER key is pressed, checkbox should search the form for all submit buttons and inputs and send a MouseClick event to the first submit button that is not disabled.

Verify that this CodePen still works.

What is the current behavior?

Checkbox emits a native submit event when the ENTER key is pressed.

What is the use-case or motivation for changing an existing behavior?

Checkbox keyboard behavior should match the native behavior on Chrome.

Which versions of AngularJS, Material, OS, and browsers are affected?

• AngularJS: 1.7.6
• AngularJS Material: 1.1.13
• OS: macOS
• Browsers: Chrome

Is there anything else we should know? Stack Traces, Screenshots, etc.

@codymikol heads up that this is related to PR #11584 and issue #11583. I will try to make a fix for this today.