Fix FP S6594 (sonar-prefer-regexp-exec): Ignore match count use case

[yassin-kammoun-sonarsource]

The rule should not suggest using Regex.exec if the returned value of String.match is eventually used to get the number of matches. It only involves getting the .length of the value, while a loop is needed in the case of Regex.exec.

const regex = new RegExp(pattern);
const matches = 'foo'.match(regex); // Currently false positive, should be compliant

/* ... */

matches.length;

/* or */

matches?.length;