improved vlc controller events & callbacks code (solid-software#216)

* updated vlc event handling code

* fix vlc error description

* renamed error const strings

* fixed a minor bug

* Avoid FlutterVlcPlayerFactory new instances onAttachedToActivity (solid-software#214)

* Avoid FlutterVlcPlayerFactory new instances onAttachedToActivity

* Avoid FlutterVlcPlayerFactory instances in registerWith

* fix error description docs

* Added onInit & onRenderer listeners

* updated docs

mark onInit & onRendererHandler as deprecated.

* updated documentation

* fix initialization value of renderer variables

Co-authored-by: Guillermo Jeremy De La Cruz Onton <[email protected]>

Update to 6 to indicate breaking change / Null-Safety

Update to 6 to indicate breaking change / Null-Safety

remove upper constraint per flutter/flutter#68143

Added isSeekable method (solid-software#175)

* fixed dart deprecation warning

added the missing async await to some platform methods

* updated example code

* fixed dart deprecation warning

added the missing async await to some platform methods

* updated example code

* added isSeekable method

fix example player widget crash if the media position becomes greater than the media duration

* fixed dart deprecation warning

added the missing async await to some platform methods

* updated example code

* revert back seekto method

* updated pubspec and changelog

* 5.0.4 release / readme and changelog

* Update flutter_vlc_player/ios/Classes/SwiftFlutterVlcPlayerPlugin.swift

Co-authored-by: Yuri Prykhodko <[email protected]>

* Update flutter_vlc_player/android/src/main/java/software/solid/fluttervlcplayer/FlutterVlcPlayer.java

Co-authored-by: Yuri Prykhodko <[email protected]>

* update example code

Co-authored-by: Yuri Prykhodko <[email protected]>

5.0.3 release / readme and changelog

Fix homepage link.

5.0.1 - fix pub.dev links

rename to match package name and update credits

fix example when it takes a long time initialize duration