Rewrite multiline strings properly

Rewrite multiline strings properly

Because the bindings rewriter works on code strings, it would leave
multiline strings across multiple lines (which is illegal in ECMAScript.

It now manually breaks them up when it sees them, by replacing a \n
character with a literal \n.

Since RewriteSignalHandler now likes to have the AST passed in too, the
related method in QDeclarativeCompiler (and its customers) have been
altered to use the QDeclarativeScript::Value instead of just a string.

Task-number: QTBUG-23387
Change-Id: Id060de37e70590c9da2a902038ed02d948fdd70f
Reviewed-by: Alan Alpert <alan.alpert@nokia.com>