Duplicate keys are valid in $jsonSchema, but are not handled in CSFLE processing.

Multiple `properties` keys of the same name are processed with a "last-wins" map assignment during encryption schema tree construction (`_propertiesChildren[std::string

] = std::move(node);` in `addChild()` in `encryption_schema_tree.cpp`). 

Similarly, multiple `patternProperties` nodes with identical regex are currently processed with a "first-wins" std::set insert in `addPatternPropertiesChild()` in  `encryption_schema_tree.h`.

Instead of dropping duplicate keys silently, which may lead to confusing or unexpected behavior for the user (such as a field's encryption information being overwritten), we should assert on duplicate keys and fail with a FailedToParse for both `properties` and `patternProperties`.