fix(fabric.parser): attempt to resolve some issues with regexp

[asturur]

It looks like the regexp we use to parse CSS may be susceptible of high CPU usage with crafted payloads.
This would make servers that use fabric to parse SVGs at risk of crash or DOS.
This PR removes the regexes and uses a simpler approach to parse style rules.

[asturur]

@JamieSlome do you want to verify if this fix your concens?

[github-actions]

Code Coverage Summary

> fabric@4.6.0 coverage:report
> nyc report --reporter=lcov --reporter=text

-----------|---------|----------|---------|---------|-----------------------------------------------
File       | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s                             
-----------|---------|----------|---------|---------|-----------------------------------------------
All files  |   83.39 |     77.1 |   86.16 |   83.11 |                                               
 fabric.js |   83.39 |     77.1 |   86.16 |   83.11 | ...,30155,30280,30360-30425,30548,30647,30864 
-----------|---------|----------|---------|---------|-----------------------------------------------

[JamieSlome]

@asturur - thanks for the bump 🤛

I am just tagging the researcher @ready-research - can you take a look at the fix here?

[ready-research]

@asturur - Yeah, proposed changes LGTM. Sorry for the late reply.

[asturur]

why i can't merge? lol

[asturur]

@ShaMan123 can you try approve this PR?