Map link custom element implementation

[prushforth]

Closes #915

• [x] create map-link.extent property structured per layer-.extent property
• [ ] ~create M.getZoomBounds(extent) and M.getBounds(extent) functions~ future work
• [ ] ~ensure that the map-link.extent is recalculated if changes occur to e.g. in-scope map-meta, map-input min/max~ future work
• [x] generate private map-link._templateVars property during tref attributeChangedCallback
• [x] construct map-link._templatedLayer during connectedCallback
• [x] when only one map-extent with image map-link is disabled in the console, the layer does not get disabled.
• [ ] ~map-extent units attribute can be named to 'projection'?~
• [x] need to check if we ever fall into this if block in getBounds()

• [ ] map-features independence - https://github.com/AliyanH/Web-Map-Custom-Element/tree/map-link-features
• [x] closes #898 in 0d77e492a0e41382a562c07564459234e638820d (Switching Local content to remote, remote to local content not yet supported)
• [x] TODO map-feature addzoomlimit, resetting layer bounds, etc.
• [ ] Need to document API use, and that it can only be used after connected to DOM
• [x] Fix bug in paging queried features

Known Issues

• [x] Vector tiles example zoom to layer does not work properly.
• [x] progressive enhancement errors
• [x] map-feature API addFeature errors

Tests Required:

• [ ] add test for min max zoom attributes for map-features
• [x] Dynamic Layer bounds test - i.e. check if layer bound gets updated when a new map-feature is added to layer
• [ ] map-feature zoom API, fallback should be initial map location can test using zoomTo on map-feature
• [ ] map-feature min, max utilizes attributes -> map-meta zoom if provided and then fallback
• [ ] removing a feature updates the Layer's bound and also the mapmlvectors bounds (when no overlapping map-meta extent exists)
• [x] empty layer's extent is projection extent/zoom + it updates once some content is added to the layer. Potential map-link tests
  • [x] extent property
  • [x] test that extent of map-link established via map-meta compares to map-link
  • [x] extent established via map-input min/max variables, according to what the docs
  • [x] say about what takes precedence (map-input takes precedence, usually)
  • [x] test that extent of map-link changes to reflect updates to map-meta and map-input min/max
  • [x] test that layer/extent is disabled if the bounds or zoom bounds of a query link go
  • [x] out of view
  • [x] test the zoomTo() function, which relies on map-extent
  • [x] test that links that shouldn't have an extent behave accordingly
  • [x] test that you can construct a map-link programmatically and have it work
  • [x] test that links in local and remote content work the same

Documentation Required

• [ ] the extent of a layer's render zoombounds incorporates map-extent->map-input
• [ ] map-link -> extent property, zoomTo() method

Future Work

• [ ] map-meta extent methods (zoomTo, etc.) - initial work at https://github.com/AliyanH/Web-Map-Custom-Element/commit/314fdc58336ed89bab5d79bfbb559172196a6857

[prushforth]

We should try to fix this bug in this branch

[prushforth]

Just going to post a couple of notes so that they don't get overlooked.

• in /experiments/painting/, the People layer is always disbled, because the MapMLLayer._mapmlvectors.zoomBounds seems to return an empty object {}. Probably something to do with addLayer and/or _resetFeatures (which is the zoomend handler).
• could _leafletLayer be renamed to e.g. _MapMLLayer for clarity? Everything is a Leaflet layer in the end and it's confusing (to me).
• committing a small change to DebugOverlay which makes looking for _leafletLayer conditional on its existence, since I believe that it comes across layers that are part of the DebugOverlay which are not added to the map by any MapML element. If confirmed, would be a good place for a comment.

[prushforth]

Discovered while re-ordering multiple extents within a layer (via drag and drop):

map-link.js:307 Uncaught (in promise) DOMException: Failed to execute 'attachShadow' on 'Element': Shadow root cannot be created on a host which already hosts a shadow tree. at MapLink._createTemplatedLink (http://.../geoserver/mapml/viewer/widget/map-link.js:3:3619)