feat(material/chips): add (optional) edit icon to input chips

[adolgachev]

Adds an optional edit icon to input chips to allow for better discoverability of editable chips over existing double-click and focus-enter to edit behavior.

The edit icon introduces concept of a leading action with an icon button similar to trailing action used for delete icon button. This can be combined with the existing avatar icon for a chip. The editable flag is preserved but is independent of the edit icon, allowing for both existing and new behavior or either one.

Updated chip demo to add option to show avatar and/or edit icon.

[github-actions]

Deployed dev-app for fe5ea55 to: https://ng-dev-previews-comp--pr-angular-components-31041-dev-jgj91wpx.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

[crisbeto]

Actually I also realized that we should add a live example for the docs site. The examples live under components-examples.

[github-actions]

Deployed docs-preview for fe5ea55 to: https://ng-dev-previews-comp--pr-angular-components-31041-docs-h4ff3yly.web.app

Note: As new commits are pushed to this pull request, this link is updated after the preview is rebuilt.

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