feat(pb-search) slots for 'search' + 'reset' controls

[JoernT]

support slots for 'search' and 'reset' controls.

This allows to create a pb-search:

• without any buttons (default)
• with native buttons
• with paper-buttons
• other elements that support the 'click' event.

Demo file (pb-search4.html) included

[github-actions[bot]]

:tada: This PR is included in version 1.3.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: