Update Validators.pattern docs to mention the use of global flag in RegExp

We should update the Validators.pattern docs to mention possible effects of using the global flag (e.g. /abc/g) in a RegExp passed as an argument. If the validator function is invoked multiple times the subsequent calls might produce unexpected results due to the lastIndex being preserved. Additional info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/test.

[AndrewKushnir]

@sonukapoor thanks for the comment. I was thinking about that too, but my understanding is that we should not change the state of the RegExp as this is something that a user controls. Using a RegExp with a global flag for validation is typically undesirable (and not needed in majority of cases), since it has unclear practical purpose in a context of validation: if there is at least one match, the validation will be treated as successful, so if there are more matches (in case a global flag is used) it doesn’t change the validation result - it will still be successful. If there are no matches (which will be true with or without the global flag) - the validation will fail. Throwing an error in case a RegExp has a global flag might be too restrictive as well, since there might be use-cases where developers rely on shifting the lastIndex property. So I think adding a paragraph into the docs is a step forward that provides more information to users and do not restrict or enforce certain logic. We can reconsider this behavior in the future in case we get more feedback. Thank you.

[AleksanderBodurri]

@AndrewKushnir I can take this issue.