add rtl support and example #206

[gowin20]

• Adds support for RTL language labels by exposing the maplibre setRTLTextPlugin method.

• Adds an example showing how to use it:

// Support RTL languages such as Arabic and Hebrew
L.esri.Vector.setRTLTextPlugin('https://unpkg.com/@mapbox/mapbox-gl-rtl-text@0.2.3/mapbox-gl-rtl-text.js');

#206/#204

[gavinr-maps]

It seems like adding this function to our library that calls setRTLTextPlugin on maplibregl is the best way to do this. Looks good!

[gavinr-maps]

Released in v4.2.2.