box: add space upgrade stubs

To implement online space upgrade, we need to add stub calls to the
following code paths and data structures:

 - struct space: add a pointer to space upgrade state.
 - struct space_opts: add a pointer to space upgrade definition.
 - CheckSpaceFormat::prepare: skip space check if the format is changed
   in the scope of space upgrade.
 - alter_space_do: check space upgrade state and fail alter if upgrade
   is in progress.
 - alter_space_commit: run background worker for space upgrade.
 - space_on_final_recovery_complete: restart upgrade after recovery.
 - result_processor: apply space upgrade transformations to tuples
   returned to the user by box functions.

We also need to:
 - Add a new error code ER_WRONG_SPACE_UPGRADE_OPTIONS, which we will
   use on error decoding upgrade options, stored in space options.
 - Load space upgrade Lua modules. The modules are supposed to define
   box.internal.space.upgrade method, which if available is used by
   box.schema.space.upgrade.
 - Add check_param, check_param_table and normalize_format helpers to
   box.internal, because we will use them from space.upgrade Lua code.

Note, the space upgrade state will be reference counted, because
background space upgrade may complete while some fiber is reading
from the upgraded space (there may be yields in Vinyl). For this fiber
to process the result correctly, it has to increment the reference
counter of the space upgrade state before reading from the space.

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