XS allows trailing comma in Expressions

[jugglinmike]

XS parses and evaluates the following input without reporting an error:

0,;

It interprets this input as though the comma was not present.

This behavior also influences ASI semantics. XS parses and evaluates the following input without reporting an error, again behaving as though the comma was not present:

0,
if(0);

Both behaviors are consistent between the Script and Module goals.

[jugglinmike]

🎉