[Eva] evast: reorganize the interface to simplify usages

src/plugins/eva/api/values_request.ml

src/plugins/eva/ast/eva_automata.ml

src/plugins/eva/ast/evast.ml

src/plugins/eva/ast/evast.mli

src/plugins/eva/ast/evast_builder.ml

src/plugins/eva/ast/evast_datatype.ml

src/plugins/eva/ast/evast_datatype.mli

src/plugins/eva/ast/evast_printer.ml

src/plugins/eva/ast/evast_printer.mli

src/plugins/eva/ast/evast_types.ml

src/plugins/eva/ast/evast_typing.ml

src/plugins/eva/ast/evast_typing.mli

src/plugins/eva/ast/evast_utils.ml

src/plugins/eva/ast/evast_visitor.ml

src/plugins/eva/ast/evast_visitor.mli

src/plugins/eva/domains/apron/apron_domain.ml

src/plugins/eva/domains/cvalue/builtins.ml

src/plugins/eva/domains/cvalue/builtins_memory.ml

src/plugins/eva/domains/cvalue/builtins_misc.ml

src/plugins/eva/domains/cvalue/builtins_split.ml