Fix metabase-lib/metadata/Metadata type (#30808)

frontend/src/metabase-lib/metadata/Field.ts

frontend/src/metabase-lib/metadata/Metadata.ts

frontend/src/metabase-lib/metadata/Metadata.unit.spec.ts

frontend/src/metabase-lib/metadata/utils/fields.ts

frontend/src/metabase-types/api/mocks/schema.ts

frontend/src/metabase-types/api/schema.ts

...in/permissions/selectors/data-permissions/data-sidebar.ts

frontend/src/metabase/admin/permissions/utils/metadata.ts

frontend/src/metabase/selectors/metadata.ts