Escape backslashes in wxJSScriptWrapper to allow strings with
backslashes in them to work again -- this was broken while implementing
support for returning values from JavaScript to C++.
See https://github.com/wxWidgets/wxWidgets/pull/741
No real changes, but just use string concatenation instead of line
continuation backslashes and also replace hard TABs with spaces.
Notice that the code is still completely unreadable as JavaScript, but
this shouldn't be a problem as nobody will see it there anyhow, so it's
quite enough to have it more readable in its string form in C++.
We can prepare the escaped code directly here, instead of waiting for
GetWrappedCode() call, this is more clear and safer as it avoids
escaping the code twice accidentally if GetWrappedCode() ends up being
called twice somehow.
While it is allowed there, it is confusing and unnecessary.
Also improve the comment explaining why do we need this output variable
name at all and why does it need to be unique.
This is a non-standard extension in the first place and the variable
name didn't make any sense too, so rename it to be standard-conforming
and actually correspond to what it contains.
