Most if not all libusb functions return UTF-8 encoded data
but hidapi functions typically take and return wide character strings.
Adapt one of the existing algorithms in the code base into a general
conversion function.

Returns libusb error names and strings
converted to wide character strings.

Store libusb error code so it can be retrieved later.

Includes the original error code as well as a context-specific message
which the libusb documentation sometimes specifies for each function.
Code which uses those functions are meant to set the contextual message
whenever possible.

The code is initialized to a success state which implies no errors yet.
The contextual error message is initialized to NULL and is not freed
when the device is closed. It is meant to point at string literals.

Sets all error data, including an optional contextual error message
which is supposed to be a non-freeable constant string
such as a string literal.

Contextual error messages are meant to be used in the cases
the libusb documentation goes into detail as to what happened.
Passing NULL will produce a message with just the libusb_error_name
and the libusb_strerror results. Passing a string literal will produce
a message that contains the additional context in addition to the error
name and message.

Set error data when send_feature_report fails, including custom messages
for the situations especially outlined in the libusb documentation for
the libusb_control_transfer function.

Compute a formatted error string containing the libusb error name,
the error message as well as any contextual information.
Return NULL if there are no errors or if memory allocation failed.