Fix Libvcx C Error Message Segfault

[hadleym]

Fixes the current libvcx vcx_error_c_message api call. In the current version of vcx_error_c_message, the memory returned via pointer is dropped at the end of the api call, causing undefined behavior when the wrappers dereference the returned pointer.

[hadleym]

@glowkey
Please review.

[Artemkaaas]

Doesn't compile on jenkins

#[repr(transparent)]
   | ^^^^^^^^^^^^^^^^^^^^

error[E0658]: the `#[repr(transparent)]` attribute is experimental (see issue #43036)

update rust version.

[jovfer]

@hadleym please fix Java wrapper too

[jovfer]

double-check Artem's suggestion on Jenkins: yes, with incremented rust version this PR can pass build stage on Jenkins for VCX (jovfer@95b7d2a).

[hadleym]

@jovfer
I will fix the Java wrapper as well as the rust version as suggested by @Artemkaaas

[glowkey]

Please hold off on merging this PR until I have had a chance to review it.

[hadleym]

@glowkey has found the correct reason for the python segfaults regarding vcx_error_c_message, and will implement a fix in his future PR.