0.119 → 0.120 — a table's container column is quill::table_column_not_leaf

The break no type checker reports: a ui.layout: table column that is not a leaf is refused under a new code. The refusal, its trigger and its message are unchanged; only the code moves, so a consumer matching the old string stops matching. flat is ui.layout's word for a typed dictionary drawn without a frame, and the column check names what it tests, FieldType::is_leaf.

Break	Surface	Action
A ui.layout: table column holding an array, object or matrix fails to load as quill::table_column_not_leaf, where it was quill::table_column_not_flat	diagnostics	Match the new code