Report and adjust AUTO_INCREMENT values in metadata commands

[JanJakes]

Summary

Adds support for reporting and adjusting AUTO_INCREMENT counters, which the driver previously ignored.

Reporting (commit 1)

SHOW TABLE STATUS, SHOW CREATE TABLE, and INFORMATION_SCHEMA.TABLES now compute the Auto_increment value live from sqlite_sequence rather than returning NULL. The counter is preserved past DELETE and reset by TRUNCATE, matching InnoDB semantics.

This retires the first half of patchWp15AdminPostAutoIncrement in WordPress, which existed to work around WP 1.5's wp-admin/post.php reading the SHOW TABLE STATUS Auto_increment column.

Adjusting (commit 2)

Three MySQL forms are now honored:

1. CREATE TABLE t (...) AUTO_INCREMENT = N — seeds the counter.
2. ALTER TABLE t AUTO_INCREMENT = N — instant; no table rebuild.
3. ALTER TABLE t <actions>, AUTO_INCREMENT = N — applied alongside other alter items.

The requested value is written as N - 1 into sqlite_sequence (MySQL stores the next value, SQLite the last used), clamped to MAX(col) so the effective counter never drops below an existing row — matching MySQL. When the table has no AUTO_INCREMENT column, the option is silently ignored, matching MySQL.

Not covered: SET @@auto_increment_increment / SET @@auto_increment_offset. These change the step and offset of generated values, not the counter, and SQLite's AUTOINCREMENT always steps by 1 — so emulating non-1 increments would require generating IDs in PHP for every insert. Out of scope here.

Tests

• testInformationSchemaTablesAutoIncrement, testShowTableStatusAutoIncrement, testShowCreateTableAutoIncrement, testShowCreateTableAutoIncrementOnTemporaryTable, testShowTableStatusFilterByAutoIncrement — reporting.
• testCreateTableAutoIncrementOption, testAlterTableAutoIncrementOption, testAlterTableAutoIncrementOptionMixedWithAlterItems, testAlterTableAutoIncrementOptionWithoutAutoIncrementColumn, testAlterTableAutoIncrementOptionAfterTruncate, testAlterTableAutoIncrementOptionOnTemporaryTable — adjustment, including MAX-clamp behavior, fast-path (no rebuild), mixed alter items, temp-vs-persistent isolation, and no-op when there's no AI column.

Notes

• sqlite_sequence has no UNIQUE constraint on name, so native upsert is unavailable; the row is maintained with UPDATE-then-INSERT (second query only runs when the first matches nothing).
• The clamp expression is inlined as an integer literal rather than a bound parameter. PDO binds PHP ints as TEXT, and SQLite's type affinity ranks TEXT above INTEGER in MAX(), which would silently produce wrong results.
• ALTER TABLE with only table options (no alterListItem) now skips the full-table copy — previously a pointless rewrite.

Test plan

• CI green.
• New tests in WP_SQLite_Driver_Metadata_Tests pass.
• Full suite (665 tests) still passes.