feat(): add ability to continue processing hardware back button events

[liamdebeasi]

blocks ionic-team/ionic-docs#1356

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Issue Number: #17824

What is the new behavior?

• Added feature to allow multiple handlers to be processed sequentially
• Added docs with examples
• Added tests

Does this introduce a breaking change?

• Yes
• No

Other information

[brandyscarney]

Is this considered a feature? Seems more like a bug fix?

Code looks good! Added @elylucas for reviewing React but looks like it should work fine.

[liamdebeasi]

@brandyscarney I made it a feature since it adds a new parameter to the callback, but if you think it's more of a bug fix I'm fine with that too.