feat: make properties panel container focusable

[jarekdanielak]

Related to https://github.com/bpmn-io/internal-docs/issues/1081

Proposed Changes

By making properties panel container focusable, user can click somewhere in the container (not only on buttons and inputs) to continue using keyboard shortcuts in the context of the panel.

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

[nikku]

Good stuff! Let us also port this to the DMN properties panel.