rust/applayer: clean visibility of export macros

rust/applayer: clean visibility of export macros

Both the macros export_tx_data_get and export_state_data_get can
generate non-pub functions as the function they generate is only used
as a pointer during registration.

Remove "pub" and "no_mangle" from the generated functions and update
the names of the generated functions to follow Rust rules as they are
no longer exported into the global C namespace.

Ticket: 7498