To be removed in the next open-source release.

Exports these functions in Eva.mli.

Used by the from plugin when option -from-verify-assigns is enabled.

Must be consistent with [define_analysis_target].

- Info (expr_node)
- IndexPI (PlusPI synonym)

For abstract domains, the valuation is now a record of three functions:
[find], [fold] and [find_loc].

Adds a function in the evaluation engine to convert Valuation maps into
these records.

New function Builtins.is_builtin_overridden that indicates whether a function
is replaced by a builtin.
This function remains correct after loading the result of a previous analysis,
and can thus be used by other plugins using Eva's results.
Thus, Db.Value.use_spec_instead_of_definition now uses this function.

In abstract.ml, the structure of compound abstract values, locations and states
carries the first class module of their leaf components as data.

Keys for abstract values, locations and states are created in structure.ml.
Shapes are created in the respective modules Value, Location and Domain
in abstract.ml.

These module definitions were previously in abstract_value, abstract_location
and abstract_domain. They are now grouped in this new file for the three
abstractions.
These module types should only be useful for the engine, and need not to be
visible in the implementation of the various abstractions.

New module type Leaf in abstract_value, abstract_location and abstract_domain
with the key identifying the module. The internal structure is no longer needed
in these abstractions, and is instead built by the engine from this key.

Keys are no longer exported outside the modules.
For abstract domains, the key is automatically created by the functor
Domain_builder.Complete from the domain name.

Many changes throughout the analyzer:
- in the engine, Abstract_value.{Internal|External} becomes
  Abstract.Value.{Internal|External}.
- in the abstractions, Abstract_value.Internal becomes Abstract_value.Leaf.

- shares and moves the functions [reduce_offset_by_validity] of Locations and
  Precise_locs into base.ml.
- replaces the boolean argument ~for_writing into the new type access, that
  represents Read, Write or No_access. Without any access, offsets must point
  into or just beyond the base validity.
- fixes the support of accesses of size 0: they are now invalid:
  + in bases with Invalid validity;
  + one past a base validity unless the base ends with an empty struct.

(blind make headers from specifications)

- Fix Value/Value#5
- Fix Value/Value#14