__splitString behaviour is not intuitive and documentation is not explicit enough

@pmouawad ([Bug 61626](https://bz.apache.org/bugzilla//show_bug.cgi?id=61626&redirect=false)):
__splitString has a counter intuitive behaviour when separator is "," (default one).

Problem 1:
Indeed, the String to split would need to be escaped which is in fact rarely the case when you need this function ?

Will String really contain:
"a\,b\,c"

Or :
"a,b,c"

Problem 2:
Also, when you by error input this:
${__split(a\,b\,c,varSplit,)}

It doesn't work because function uses empty separator which is wrong, as documentation says this parameter defaults to ",". So function should just ignore this empty .

Problem 2 can be fixed.
How to fix problem 1 ?

OS: All