MDEV-36986 Support tracing arrays of primitive types

[bsrikanth-mariadb]

Single_line_formatting_helper accumulates array elements that may fit on one line, and printed all of them quoted when flushing numbers, booleans and nulls thus came out as JSON strings:

"depends_on_map_bits": ["0"] instead of [0]

Solution is to:

Remember per element whether it arrived via add_escaped_str() (a string, quote it) or add_unquoted_str() (a number, boolean or null, don't), in a parallel quoted[] array reset together with the buffer, and honour it in both flush paths. This also fixes disable_and_flush(), which called add_str() and so escaped the buffered strings a second time.

add_size() output stays quoted: it may carry a unit suffix ("2KiB").

While at it:

• Json_writer_array::add(ulonglong) cast to longlong, printing values above LLONG_MAX as negative. Use add_ull(). add(size_t) had the same bug and is compiled out on _WIN64, so fixing only one would have made the output platform-dependent.
• on_add_str() now enforces MAX_ELEMENTS instead of only asserting it, so quoted[] cannot be overrun in a release build if the line length accounting ever changes.

opt_context_schema.inc: rec_per_key holds numbers now, not strings. Also fix two syntax errors that left the schema invalid JSON, so it is usable once MDEV-38033 enables the JSON_SCHEMA_VALID() check in run_query_twice_and_compare_stats.inc.