Allow Customization of OpenLayers Format Parameters

[ambrazasp]

As described in #407, format option is set as new MVT() for OpenLayers.

However in some cases you need to rewrite format and pass MVT options.

There is two solutions:

• Pass MVT options
• Pass custom formater

In this case it's easier to go with 2nd option (passing custom formatter).

From now on you can do something like this:

new PMTilesVectorSource({
  ..., 
  format: new MVT({
    featureClass: ol.Feature,
    idProperty: 'customId',
  }),
})