Highlight feature border on hover in `clickFeatures` mode

[jessicamcinchak]

This will help prevent clicking un-intended features, and then needing to double-click to un-select

Potentially combine with a tooltip with feature info if we have useful data fields available

Inspired by https://applicantmaps.planning.nyc.gov/

[jessicamcinchak]

Started thinking about this on branch jess/highlight-feature-hover. Since features need to be queried on every mouse move to highlight (they aren't all pre-loaded in the basemap), I realized we'll hit our current OS Features API rate limit pretty quickly. May make sense to bookmark this until we sort out better API keys through a central partner.