fix: resolve schema-qualified table names in getFieldData() and protectIdentifiers()

[paulbalandan]

Description

getFieldData() returned no fields for a schema-qualified table name (e.g. public.jobs). Found while reviewing #10601 and #10602, whose batch casts depend on it.

• BaseConnection::protectDotItem() did not strip the escape character before checking for the prefix, so an already protected "tenant"."db_jobs" was prefixed again. The builders pass protected table names to getFieldData(), so every driver got a mangled name.
• Postgre and SQLSRV ignored the schema segment, and SQLite3 produced an invalid PRAGMA. MySQLi and OCI8 already handled a clean schema.table.

Unqualified names behave as before. Tests cover the protectIdentifiers() cases and getFieldData() with a qualified name on all drivers.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

With QUOTED_IDENTIFIER OFF, the SQLSRV driver sets $this->escapeChar to ['[', ']']. Passing this array as the second argument to trim() causes a TypeError when processing dotted identifiers. I verified that protectIdentifiers('jobs.id') returned [jobs].[id] before this change and now throws. We should handle the array form of escapeChar and add a regression test.

[michalsn]

This case also failed before the PR, but it appears to be a missing case within the intended fix. With an empty DBPrefix, the normalized $parts are not joined back into $item, so getFieldData('"public"."jobs"') still passes the quotes into the metadata query and returns no columns. Since Query Builder passes protected table names, could we cover this path too and add a test for a quoted, schema-qualified table name with an empty prefix?