Options/selection elements

Problem/Motivation

Part 3 of splitting #3595219: 3.0 Exploration. This issue completes support for options-based elements — select, radios, checkboxes, tableselect and the term-reference selects — whose option handling is currently incomplete.

Gaps in 3.x:

• The empty/placeholder option of a select (#empty_option / #empty_value) is not exposed.
• Checkboxes' "check all / none" affordance (#options_all / #options_none values) is not represented.
• Option randomization (#options_randomize) is neither exposed nor handled — randomized option order leaks into the resolved list non-deterministically.
• Nested (grouped) options lose their group label.
• Options of disabled elements are dropped.
• The "options display" settings (how options are laid out, e.g. side-by-side) are not exposed.
• Table-like elements (tableselect) and term-reference selects do not resolve their real option set.

Proposed resolution

• Introduce a GraphQL interface for select-style elements and expose the empty option (value + label).
• Introduce a checkboxes interface exposing the "all" / "none" option values.
• Expose optionsRandomize and, when resolving, "unshuffle" the options to a stable order so the exposed list is deterministic while still signalling that randomization is configured.
• Carry the groupLabel through nested option groups on WebformElementOption.
• Resolve options even when the element is disabled.
• Expose the options-display setting via a WebformOptionsDisplay enum.
• Resolve real options for table-like elements and for WebformElementWebformTermSelect (including the existing depth handling).

All option resolution goes through src/Plugin/GraphQL/DataProducer/WebformElementOptions.php, with the per-element types/interfaces generated in src/WebformSchemaBuilder.php and wired in WebformExtension.php.

Remaining tasks

• Add the select/checkboxes interfaces and the WebformOptionsDisplay enum (src/Enum/WebformOptionsDisplay.php); wire into WebformSchemaBuilder.php and WebformExtension.php.
• Extend WebformElementOptions.php: empty option, all/none, randomize + unshuffle, groupLabel, disabled-element options, table-like and term-select option resolution.
• Tests: CheckboxesTest, RadiosTest, SelectOptionGroupsTest, DisabledOptionsTest, OptionsDisplayTest, RandomizedOptionsTest, TableSelectTest, TermSelectTest, plus the matching tests/queries/*.gql fixtures and additions to the shared test-form fixture.

API changes

Additive: new select/checkboxes interfaces and fields (empty option, all/none values, optionsRandomize, groupLabel, options display), and a new WebformOptionsDisplay enum. No fields removed.

Release notes snippet

Options-based elements (select, radios, checkboxes, tableselect, term selects) now expose their empty option, check-all/none values, options-display setting and group labels, resolve options even when disabled, and report option randomization with a deterministic order.