Updated code to use Dart 3.x features and other improvements

[4.0.0-beta.1]

Breaking Changes

• PlaceSearch and ReverseGeoCoding classes are now merged into one class called GeoCoding with two methods getPlaces and getAddress since both of them are using the same API.

New Features

• MapBox's new SearchBox API is added to the package.
• Overal code refactoring

• Fixed Static Image URL generation issue

• Added Proximity Type to Search (As per MapBox API we can use location or ip address to get the nearest results)
• Optimized the code and added tests for reverse geocoding class too
• Fixed some issues regarding static image to use custom markers
• Changed zoom level to use double instead of int(Fix #61)

• Homepage URL fixed

• PlaceType enum to string conversion fixed

• Added Places type to filter Search [PR #48]

• Migrate to null safety [Pull Request #43]
• Removed Color dependency [Pull Request #44]

• Updated http dependency (PR #41)

• Updated dependencies
• Major missing feature added
  • Maki Icons can now be used in marker icon

PR by @lukas-h

Some breaking Changes

• renamed

   MapBoxStaticImage 
  

  to

  StaticImage 
  

  to make the naming in this library more consistent

Improvements

• simplified the url serialisation
• added the auto attribute to static images
• added simple unit tests for static images

• Added Missing Address Attribute to the fetched MapBoxPlace Data (PR by @ juampiq6).

• Breaking changes(migration from v1.x ro v2.0)

• Added Places Search for querying places by text.
• Fixed limit and country parameters for ReverseGeocoding.

• Added 'address' property to the Properties class.

• Search text in search Widget localized

• Reverse Geocoding query type set to dynamic(String or double)

• Reverse Geocoding returning empty list bug Solved

Feature:

• Reverse Geocoding Added

Feature:

• add defaultPathPolyline and add assert(Merge Request)

Initial release.

Feature:

• Places Search with prediction
• Static Image with marker
• Static Image without marker
• Static Image with Polyline path