[Ada] Store the Ada task list in per-inferior data

[Ada] Store the Ada task list in per-inferior data

Instead of storing "the" Ada task list using a static global
in ada-tasks, this patch stores that information inside
per-inferior data.

We also add in the per-inferior data the location and type of
data used in the runtime to store that task list.  Previously,
this information was saved as a static variable in one of the
functions, but this approach has the major flaw that it does
not handle multi-inferior debugging.

gdb/ChangeLog:

        * ada-tasks.c (ada_tasks_check_symbol_table, task_list): Delete.
        (enum ada_known_tasks_kind, struct ada_tasks_inferior_data): New.
        (ada_tasks_inferior_data_handle): New static global.
        (get_ada_tasks_inferior_data): New function.
        (ada_get_task_number, get_task_number_from_id, valid_task_id)
        (ada_get_environment_task, iterate_over_live_ada_tasks)
        (add_ada_task, read_known_tasks_array, read_known_tasks_list):
        Adjust.
        (ada_set_current_inferior_known_tasks_addr): New function.
        (read_known_tasks, ada_build_task_list, short_task_info)
        (info_tasks, info_task, info_tasks_command, task_command_1)
        (task_command, ada_task_list_changed): Adjust.
        (ada_tasks_invalidate_inferior_data): New function.
        (ada_normal_stop_observer, ada_new_objfile_observer): Adjust.
        (_initialize_tasks): Set ada_tasks_inferior_data_handle.
        * ada-lang.h (struct inferior): Add declaration.
        (ada_task_list_changed): Update profile.
        * remote-wtx-pd.c: #include "inferior.h".
        (switch_to_pd_internal): Update call to ada_task_list_changed.