fix: [#1308] Fix a bug of multiple fallbacks of custom property

[odanado]

Fix: #1308

The previous code was incorrect in its use of RegExp.prototype.exec, and the regular expression matching was performed only once.

RegExp.prototype.exec is difficult to use correctly because it is a stateful API.
I modified the logic using String.prototype.matchAll as described in MDN.

In addition, String.prototype.matchAll() helps to simplify matching multiple parts of a string (with capture groups) by allowing you to iterate over the matches.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec#description

[capricorn86]

Thank you for contributing @odanado! 🌟

matchAll() will execute a find all and return an iterator for each loop in the while statement, which will not have very good performance.

I instead corrected the exec() to run on the modified value, which solved the problem.

[capricorn86]

Sorry @odanado, I was a bit fast. exec() won't work, so I changed it to this implementation using match() instead (which should also have good performance):
#1312

Not sure why the unit tests passed in the PR 🤔