Clean up hlds_module.m.

compiler/hlds_module.m:
    Put related fields of the module_sub_info next to each other.

    Some of those fields contained lists that were built reversed,
    in order to avoid O(N^2) behavior when repeatedly adding new items
    to the end of the list. Replace these with cords, which did not exist
    when those fields were first added.

    Give some fields and their getter/setter predicates more descriptive
    names.

    Separate out both the declarations and definitions of the getter and
    setter predicates, and put them into the same order as the (updated)
    order of the fields. Put the utility predicates (those that are more
    complicated than just getters or setters) into an order based on
    what fields they work on, following the same order.

    Improve the operation of some of the utility predicates, e.g. replacing
    a nondet predicate with a det predicate returning a set.

    Delete an unused type.

    Conform to the changes in the modules imported by hlds_module.m,
    e.g. pred_table.m, prog_data.m and prog_foreign.m.

compiler/pred_table.m:
    We used to store the set of valid pred ids as two lists, again to avoid
    O(N^2) behavior. Replace the two lists with a set. This allows
    looking up the set *without* updating the pred_table, or, when
    the pred_table is within the module_info, updating the module_info.

    Instead of allowing callers to replace the set of valid pred ids wholesale,
    enforce the documented invariant on that set by only allowing deletions.

    Conform to the changes above.

compiler/add_pragma.m:
compiler/bytecode_gen.m:
compiler/check_typeclass.m:
compiler/compile_target_code.m:
compiler/cse_detection.m:
compiler/dead_proc_elim.m:
compiler/deep_profiling.m:
compiler/dep_par_conj.m:
compiler/dependency_graph.m:
compiler/deps_map.m:
compiler/det_analysis.m:
compiler/distance_granularity.m:
compiler/equiv_type_hlds.m:
compiler/erl_code_gen.m:
compiler/exception_analysis.m:
compiler/export.m:
compiler/float_regs.m:
compiler/foreign.m:
compiler/higher_order.m:
compiler/hlds_module.m:
compiler/inlining.m:
compiler/intermod.m:
compiler/introduce_parallelism.m:
compiler/lambda.m:
compiler/liveness.m:
    Conform to the changes above.

    In many places, the change to how the valid pred ids are stored
    allows us to avoid creating new module_infos.

    In some places, fix style issues I noticed while working on the above.

compiler/llds.m:
compiler/mercury_compile_llds_back_end.m:
    Conform to the changes above.

    Move a type from llds.m to mercury_compile_llds_back_end.m, since
    only the latter uses it.

compiler/prog_data.m:
compiler/prog_foreign.m:
    Replace some types that used to hold reversed lists with cords.

    In prog_foreign.m, represent the two kinds of foreign code that
    do NOT define procedures with similarly named types.

    Delete a type (user_foreign_code) that duplicated another type.

    Replace an equivalence type with a notag type, for safety.

compiler/recompilation.usage.m:
compiler/typecheck.m:
compiler/typecheck_errors.m:
    Now that we have direct access to the set of visible modules,
    simplify the logic of some code dealing with those modules.

compiler/module_imports.m:
    Put some related fields next to each other.

compiler/llds_out_file.m:
compiler/make.dependencies.m:
compiler/make.module_dep_file.m:
compiler/make_hlds_passes.m:
compiler/mark_tail_calls.m:
compiler/mercury_compile_front_end.m:
compiler/mercury_compile_middle_passes.m:
compiler/ml_proc_gen.m:
compiler/mlds.m:
compiler/mlds_to_c.m:
compiler/mlds_to_cs.m:
compiler/mlds_to_il.m:
compiler/mlds_to_java.m:
compiler/mlds_to_managed.m:
compiler/mode_constraints.m:
compiler/modes.m:
compiler/modules.m:
compiler/passes_aux.m:
compiler/polymorphism.m:
compiler/post_typecheck.m:
compiler/pred_table.m:
compiler/proc_gen.m:
compiler/prog_item.m:
compiler/purity.m:
compiler/rbmm.condition_renaming.m:
compiler/rbmm.execution_path.m:
compiler/rbmm.live_region_analysis.m:
compiler/rbmm.live_variable_analysis.m:
compiler/rbmm.points_to_analysis.m:
compiler/rbmm.region_arguments.m:
compiler/rbmm.region_instruction.m:
compiler/ssdebug.m:
compiler/stm_expand.m:
compiler/stratify.m:
compiler/structure_reuse.analysis.m:
compiler/structure_reuse.direct.m:
compiler/structure_reuse.domain.m:
compiler/structure_sharing.analysis.m:
compiler/structure_sharing.domain.m:
compiler/switch_detection.m:
compiler/tabling_analysis.m:
compiler/term_constr_initial.m:
compiler/term_constr_main.m:
compiler/termination.m:
compiler/trailing_analysis.m:
compiler/trans_opt.m:
compiler/try_expand.m:
compiler/type_constraints.m:
compiler/untupling.m:
compiler/unused_args.m:
compiler/write_deps_file.m: