Validate a signal name. This can be useful for dynamically-generated signals which need to be validated at run-time before actually trying to create them.
See [canonical parameter names][canonical-parameter-names] for details of the rules for valid names. The rules for signal names are the same as those for property names.
The canonical name of the signal.
|The data is owned by the caller of the function.|
|The value is a NUL terminated UTF-8 string.|