refactor: make FlutterMap.options an optional parameter

[josxha]

This is a really tiny change but a huge quality of life change - at least for me. 😅

[JaffaKetchup]

LGTM, although we may want to consider whether the current default values are useful. Thanks!

[VittorioParagallo]

I'm not sure it depends from this, with versions 7 i got an assertion exception "flutter map 'newOptions != value.options': Should not update options unless they change"
This happens when:

• i show a map
• open a dialog
• i close the dialog and the error pop up.
  reverted on v6.1, no more troubles.