fix($parse): allow for new lines in expr when promise unwrapping is on

Previously, when unwrapping promises was set to `true`,
an error would occur if a parsed expression had a
new line in it.
This was because when generating the `evaledFnGetter` code,
a new line in an parsed expression would create a new line
in a JS string in that code, which is illegal. That is:
```js
pw("A+
B")
```