Pb collapse right

[JoernT]

feat(pb-collapse): icon can be positioned on the right by adding a CSS class 'icon-right'

When using e.g. in mobile menus it can be desirable to put the icon on the right side. E.g TEI-Publisher index page.

Apologies for the broken diff - couldn't find a way to commit CRLF from my machine and line-endings should be LF in the repo anyway but it is CRLF on master. If that's not acceptable we probably have to fix it on master before.

My other PR (line-endings) should fix that problem for the future. Not sure but probably can even resolve this PR when applied before.

The actual changes are just 2 CSS additions:

:host {
                display: block;
>>>                position: relative;
            }

and ``` :host(.icon-right) iron-icon { position: absolute; right: 0; }

[github-actions[bot]]

:tada: This PR is included in version 2.2.0 :tada:

The release is available on:

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

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