[Ada] Make the exception_support_info data per inferior.

[Ada] Make the exception_support_info data per inferior.

The ada-lang module was using a static global called "exception_info"
for all inferiors.  But each inferior might be different, and thus
this patch makes this data per-inferior.

gdb/ChangeLog:

        * ada-lang.c (struct ada_inferior_data) [exception_info]:
        New field.
        (exception_info): Delete.
        (ada_exception_support_info_sniffer): Get exception_support_info
        data from our per-inferior data.  Adjust code accordingly.
        (ada_unhandled_exception_name_addr_from_raise): Likewise.
        (ada_exception_name_addr_1, ada_exception_sym_name): Ditto.
        (ada_executable_changed_observer): Delete.
        (_initialize_ada_language): Remove call to
        observer_attach_executable_changed.