Summary:
This adds a new jsi API prepareJavaScript. This accepts the same
parameters as evaluateJavaScript() but does not evaluate anything; instead
it returns a new object PreparedJavaScript which can itself be evaluated,
via the new API evaluatePreparedJavaScript().
There is a new empty class PreparedJavaScript which may be subclassed by
each Runtime variant to store its particular prepared form.
Reviewed By: mhorowitz
Differential Revision: D10491585
fbshipit-source-id: 702b9e23f2ff03d71a8ab17efb7e154b16dd8e87
Peter Ammon