Improve search in large diagrams

[philippfromme]

Proposed Changes

• do not set zoom to 1
• reduce padding below search
• add custom marker to preselected element

Related to https://github.com/bpmn-io/bpmn-js/issues/2233 Related to https://github.com/camunda/camunda-modeler/issues/4538

Checklist

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

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

[nikku]

Try out via

npx @bpmn-io/sr bpmn-io/bpmn-js -l bpmn-io/diagram-js#search-improvements-next

[nikku]

@GeethaParthasarathy FYI :)