fix: strip the table prefix correctly when rebuilding a SQLite3 table

[karlgray]

Fixes #10508
SQLite cannot alter or drop a column in place, so SQLite3\Table rebuilds the whole table and recreates its foreign keys from the metadata it collected. That metadata holds prefixed table names, and createTable() stripped the prefix with trim($name, $this->db->DBPrefix).

trim()'s second argument is a set of characters, not a prefix. It removes any of those characters from either end of the string, repeatedly, so with the prefix db_ it turns db_bandit_fk into andit_fk — the leading b of the table's own name is eaten as well, and characters are stripped from the end too.

The rebuilt table's foreign keys then reference tables that do not exist. Nothing fails at that point, because foreign key enforcement is off for the duration of the rebuild; the error surfaces at the next write to the referenced table, naming a table that appears nowhere in the schema. Whether a given table is affected depends on which characters its name happens to begin and end with, so most tables come through untouched.

Strip the prefix the way fromTable() in the same class already does.

The existing tests could not catch this: AlterTableTest builds its own connection without a DBPrefix, and the damage is invisible until the constraint is used. The regression test therefore sets a prefix and names the referenced table so that it begins with a character the prefix also contains, which is what makes the bug reproduce.

Description
Explain what you have changed, and why.

Checklist:

• Securely signed commits
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• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[mergeable]

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[michalsn]

Overall, it looks good. Thank you!