fix(chips): don't throw when chip models are recursive, complex objects

[Splaktar]

PR Checklist

Please check that your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added or this is not a bug fix / enhancement
• Docs have been added, updated, or were not required

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Enhancement
[ ] Documentation content changes
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

If the model objects passed to md-chips include recursive structures (i.e. they include something like {value: 'Orange', parent: chipList}, then parsing them for announcements or displaying them in aria-labels throws an exception.

Issue Number:
N/A

What is the new behavior?

• improve basic demo and md-chip-remove directive docs
• no longer parse JSON object
  in order to try to provide some useful identifier in messages

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information