better support for hi-res/retina screens

[mprins]

POI

• On high-resolutions screens the POI icons can be very small; we already have scaling in place using iconScale at

  dokuwiki-plugin-openlayersmap/script.js

  Line 249 in 590af60

  const iconScale = 1.0;

  
  It is currently fixed at 1.0 where it should take into account the Window.devicePixelRatio eg. const iconScale = window.devicePixelRatio;

WMS

• Some WMS's have a vendor specific DPI parameter that we could add

TMS

• Some tile providers have retina (@2x) available, eg. Stadia maps

[mprins]

some examples and notes for WMTS / TMS:

• https://openlayers.org/en/latest/examples/wmts-hidpi.html
• https://openlayers.org/en/latest/examples/xyz-retina.html
• https://stackoverflow.com/questions/61150507/openlayers-with-osm-retina-tiles-text-too-small
• https://gis.stackexchange.com/questions/231195/openlayers-hidpi-retina-screen-with-standard-resolution-raster-tiles#
• https://stackoverflow.com/questions/61150507/openlayers-with-osm-retina-tiles-text-too-small/61160142#61160142

[mprins]

probably needs #38