Currently unused apparently

Towards consolidating all array bsearch/...

Usermanual: clusters chapter; add brief grapheme definition and clarify monotonous cluster handling.

Towards consolidating all array bsearch/...

Don't canonicalize '@' to '-' in language tags

Fixes #1406.

Geeza Pro for example, relies on that for fancy mark positioning.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1405

[use] Fix reordering

Affects morx/kerx run-time only currently.  Will adjust their sanitize next.

Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11400

See comment.

Supercedes https://github.com/harfbuzz/harfbuzz/pull/1401
Fixes https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11366

This concludes null-size enforcement changes

See comments.

Since min_size is 0, Null() still accepts this type.