<map-input>, <map-link>, and <map-extent> custom element development

[AliyanH]

• <map-input> custom element development
  • create classes for different map-input attribute 'type' ('height', 'width', 'zoom', 'hidden', 'location')
  • for each input type class, provide a validateInput() method that is called by the map-input's checkValidity() and reportValidity() methods
  • for each input type class, provide a getValue() method that is used by the map-input as a property - (<map-input>.value)
• <map-link> custom element development
• <map-extent> custom element development

Issues/problems derived from #873

• move createAndAddTemplatedLayers from on add in mapmlLayer to process content similar to how we handler other layer types

[AliyanH]

Continuing in #887