fix: Connection::getFieldData() default value convention for SQLSRV and OCI8

[michalsn]

Description
This PR fixes values returned by the Connection::getFieldData() method for the default field.

In OCI8, Oracle may add trailing spaces to DATA_DEFAULT for NOT NULL columns - a known behavior. For confirmation, see this Stack Overflow thread.

In SQLSRV, default values are returned in their native format, which is correct by design. However, since we provide a database abstraction, this PR normalizes default values to match the format used by other handlers. This ensures that retrieved metadata can be safely reused when modifying table fields, without introducing inconsistencies.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[michalsn]

Thank you @paulbalandan and @neznaika0