fix(fabric.util): unwanted mutation in fabric.util.rotatePoint

[asturur]

The function subctratEquals is mutating the original point, this is an issue of the point class where half method mutate, half don't.

This fixes the bug for the rotate point method, since returning a new point and mutating the input does not make sense.

close #7055

[github-actions]

Code Coverage Summary

> fabric@4.5.0 coverage:report /home/runner/work/fabric.js/fabric.js
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |   82.94 |    76.96 |   85.75 |   82.64 |                                               
 fabric.js |   82.94 |    76.96 |   85.75 |   82.64 | ...,29686,29811,29891-29956,30079,30178,30395 
-----------|---------|----------|---------|---------|-----------------------------------------------