The Value class currently exposes a getString() method, and has a private getStringData() method that does not do type checking.

Many callers just need to read and compare the value of a string stored in a Value, so would benefit from the StringData version of this interface. We should expose a version of getStringData that does type checking. Since a StringData is just a reference to a string owned elsewhere, such a method could potentially be used incorrectly in a line of code such as:

auto myString = doc["stringField"].getStringData();  // Returning pointer to memory about to be de-allocated.

This should be avoided by deleting the r-value override of getStringData(). As part of this work, we should consider auditing existing callers of getString() to see if they could use getStringData() instead and see a performance improvement.