Use GeoServer's minimum and maximum image generation width and height for serialized width and height inputs

[prushforth]

Background

When generating a <map-extent> for an image-based map, the current MapML extension serializes two <map-input>s which reflect the standard width and height WMS parameter values. Such inputs are serialized to support GetMap and GetFeatureInfo request templates, and (currently) have hard-coded min and max attribute values:

...
    <map-extent  units="OSMTILE">
      <map-input name="z" type="zoom"  min="0" max="18"/>
      <map-input name="xmin" type="location" rel="map" position="top-left" axis="easting" units="pcrs" min="1.6011619366020126E7" max="1.6528622369542673E7"/>
      <map-input name="ymin" type="location" rel="map" position="bottom-left" axis="northing" units="pcrs" min="-5411138.5986247435" max="-4804213.1199940005"/>
      <map-input name="xmax" type="location" rel="map" position="top-right" axis="easting" units="pcrs" min="1.6011619366020126E7" max="1.6528622369542673E7"/>
      <map-input name="ymax" type="location" rel="map" position="top-left" axis="northing" units="pcrs" min="-5411138.5986247435" max="-4804213.1199940005"/>
      <map-input name="w" type="width" min="1" max="10000"/>
      <map-input name="h" type="height" min="1" max="10000"/>
      <!-- If the layer is queryable per the GeoServer catalog, a query link template and associated variables should be serialized -->
      <map-link  rel="image" tref="http://example.org/geoserver/wms?request=GetMap&crs=EPSG:3857&service=WMS&bbox={xmin},{ymin},{xmax},{ymax}&layers=tasmania_state_boundaries&styles=green&format=image/png&width={w}&language=en&version=1.3.0&transparent=true&height={h}"/>
      <map-input name="i" type="location" axis="i" units="map"/>
      <map-input name="j" type="location" axis="j" units="map"/>
      <map-link rel="query" tref="http://example.org/geoserver/wms?request=GetFeatureInfo&query_layers=tasmania_state_boundaries&crs=EPSG:3857&bbox={xmin},{ymin},{xmax},{ymax}&language=en&version=1.3.0&transparent=true&service=WMS&layers=tasmania_state_boundaries&width={w}&x={i}&feature_count=50&y={j}&styles=green&info_format=text/mapml&height={h}"/>
    </map-extent>
...

Requirement

All width and height inputs should be serialized with the min and max attribute values in effect for the GeoServer system, if such limits indeed exist.

(Possible) Reference

<map-input type="height" name="h" min="16" max="2048"></map-input>