Allow upcasting to be optional in tools

Based on discussion with multiple people on this, it will be opt-in for YAML and JSON via new data types.

The merge also have some code cleanup, but the important part is the YAML and JSON converters.

I have tested this issue using a YAML string as input to a tool.

If the data type of the tool property is set to 'string', then
$this->getContextValue('property_name') returns the YAML string value unmodified.

When the data type is set to 'yaml_as_string',
$this->getContextValue('property_name') returns the array corresponding to the YAML.

Similarly, if a JSON string is given as input and the data type of the tool property is set to 'json_as_string',
$this->getContextValue('property_name') returns the result of json_decode().

So, moving this to RTBC.