Develop onSubmitted callback and customization of boxShadow, textField, and icon colors.

[stevenrobson]

Added the missing onSubmitted callback.
Option to change icon colors.
Option to change text area color when search bar opens.
When user taps X and the search field is empty the bar closes.

example usage. works great as a search in an AppBar.

AnimSearchBar(
   color: const Color.fromARGB(0, 12, 162, 231),
          
   searchIconColor: Colors.white,
   textFieldColor: Colors.white,
   textFieldIconColor: Colors.blue,
   boxShadow: false,
   onSubmitted: (value) => print("submitted: $value"),

   width: MediaQuery.of(context).size.width - 100,
   textController: textController,
   onSuffixTap: () {},
)

[Jhakiz]

These are exactly what am looking for; thank you @stevenrobson.
This pull request improves really this package. The onSubmit callback and TextField color are two feature i missed in this.