<map-feature> click() method

[prushforth]

• should invoke the properties popup, if available
• should invoke the last <map-a> (in document order)

worked on in #873, not closed.

[yhy0217]

should invoke the properties popup, if available

Currently working

should invoke the last (in document order)

There is a test case in featureLinks.test.js, but the map-feature click() will invoke all the <map-a> links inside the <map-feature>. Currently, there is no test for this functionality.