feat(Group): render selected objects

[ShaMan123]

This is here to hold the _renderObjects logic in case we shall need it
View diff

[github-actions]

Code Coverage Summary

> fabric@5.1.0 coverage:report
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |   82.97 |    76.03 |   85.66 |    82.7 |                                               
 fabric.js |   82.97 |    76.03 |   85.66 |    82.7 | ...,30637,30762,30842-30907,31030,31129,31365 
-----------|---------|----------|---------|---------|-----------------------------------------------

[ShaMan123]

closing this in favor of a simpler approach

- this._objects[i].render(ctx);
+ this._objects[i].group === this && this._objects[i].render(ctx);

if object is part of active selection it's group property will be equal to the active selection