Move base of term_io.m to X_to_string, write_X, format_X.

library/term_io.m:
    Move the base operations of term_io.m to the structure we use
    in parse_tree_out*.m in the compiler, where for every type X,
    there is a function X_to_string, and two predicates write_X and format_X,
    with the former operating on I/O states, and the latter operating on
    arbitrary streams. The idea is to apply the "don't repeat yourself"
    principle by having both X_to_string and write_X just call format_X.

    Apply that principle here as well, with one minor exception,
    which is that for some values of X, both write_X and format_X are
    implemented in terms of X_to_string.

    Impose the X_to_string, write_X, format_X naming scheme. The ancient code
    already in term_io.m had (each for some values of X) had

    - some of these functions/predicates missing
    - inconsistent names, in that write_X/N did I/O while write_X/(N+1)
      wrote to arbitrary streams
    - names that were inconsistent in another way, in that write_X/N did
      I/O of values of type X, but the function to convert X to string
      was NOT named X_to_string.

    Keep some of the misnamed functions around permanently, because
    some of the names for fitting into the new scheme, such as
    "escaped_string_to_string", would be strange.

    Keep the rest of the misnamed functions and all the misnamed predicates
    around temporarily, with commented-out obsolete pragmas. I expect
    to make these pragmas active when the rest of term_io.m is converted
    to this scheme.

    To prepare for that, use string.builder, not string, as the
    stream.writer instance to implement X_to_string, because of its
    better algorithmic complexity, which is needed mainly for terms
    of nontrivial size.

    Consistently put operations on each X in the order X_to_string,
    write_X and format_X.

NEWS.md:
    List all the new predicates and functions.

configure.ac:
    Require the installed compiler to contain the fix which allows
    a typespec pragma for an obsolete predicate or function.

browser/interactive_query.m:
compiler/hlds_out_util.m:
compiler/parse_tree_out_clause.m:
compiler/parse_tree_out_cons_id.m:
compiler/parse_tree_out_info.m:
compiler/parse_tree_out_pragma.m:
compiler/parse_tree_out_sym_name.m:
compiler/parse_tree_out_type_repn.m:
library/pretty_printer.m:
library/stream.string_writer.m:
library/string.builder.m:
mdbcomp/trace_counts.m:
    Update all references to the newly-obsolete predicates and functions.

library/string.to_string.m:
    Improve variable names.

browser/interactive_query.m

@@ -624,7 +624,7 @@ write_comma_var(OutputStream, Var, !IO) :-
 
 write_module_import(OutputStream, ModuleName, !IO) :-
     io.write_string(OutputStream, ":- import_module ", !IO),
-    term_io.quote_atom(OutputStream, ModuleName, !IO),
+    term_io.format_quoted_atom(OutputStream, ModuleName, !IO),
     io.write_string(OutputStream, ".\n", !IO).
 
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