isWhiteSpace works by trimming the entire string. This works, but in the
context we use it, this is a lot of unnecessary work.
At this point we know that `+x === 0` and we want to know if that's
because x is empty or because it actually contains 0, hence we can use
a loop that just checks for a 0 existing in the string. This relies on
the assumption that there is no x such that:
+x === 0 && x.trim().length !== 0 && !x.includes('0')
In a very biased microbenchmark (https://scratch.mit.edu/projects/788352711)
this results in a 10% performance improvement.
This also will allow us to resolve https://github.com/TurboWarp/scratch-vm/issues/115
in a later commit.
Thomas Weber