<docs>: Add breaking change warning

[hoeni]

add warning about changed space key in inputs

#16664

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
docs update

What is the current behavior? (You can also link to an open issue here)

What is the new behavior (if this is a feature change)?

Does this PR introduce a breaking change?
No. It warns about an existing breaking change :-)

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Fix/Feature: Docs have been added/updated
• Fix/Feature: Tests have been added; existing tests pass

Other information:

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[hoeni]

I signed it.

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[petebacondarwin]

Breaking changes can be "added" to the log, but we should still keep the original commits under the Bug Fixes heading.

[gkalpak]

We shouldn't land this imo. We should either fix the breakage (see #16664 (comment)) or revert the change.

[Narretz]

We've changed the behavior so that the default is not prevented when click is triggered from an interactive element. This will land in 1.7.4. If you have already used ng-aria-ignore or ng-prop-click, you should keep it this way, because it's better for aria overall.