Added decoration builder

[Sourav-Sonkar]

#107
Decoration need to have access target property,as if we need to pass a custom shape , then we need get access to the target property.

Suggestion to have a call back method which provides target in the supertooltip

typedef DecorationBuilder = Decoration Function(
  Offset target,
);

[bensonarafat]

Thank @Sourav-Sonkar for your contriubtion
Let me check it out.

[Sourav-Sonkar]

@bensonarafat Should i remove the Deprecated tag or remove the decoration parameter to fix the lint??

[bensonarafat]

@Sourav-Sonkar
Can't we keep both?
And set an assert. So they cant use both as the same time

[Sourav-Sonkar]

@Sourav-Sonkar Can't we keep both? And set an assert. So they cant use both as the same time

@bensonarafat we can keep both ... but i think it would made more sense to keep DecorationBuilder only...as both will be returning decoration only

[Sourav-Sonkar]

@bensonarafat removed decoration parameter

[bensonarafat]

Great @Sourav-Sonkar
Could you also add an example readme, on how this can be used?
So, this can help others
thanks

[Sourav-Sonkar]

@bensonarafat add documentation please check

[bensonarafat]

Great @Sourav-Sonkar
I will merge it tomorrow.
thanks