feat(forms): resolve external labels to inner control of form controls

[rkaraivanov]

Description

Form-associated controls are the labellable element, so external associations target the host rather than the inner native control (<input>/<textarea>) that assistive technologies expose. Resolve the host's ElementInternals.labels onto the inner control so external labels (via for/id IDREF or by nesting) reach the AT-exposed element and focus delegation works on label activation.

• input-base / date-time-input.base: add internal _labelElements state and a _resolvedLabelElements getter feeding the native input's ariaLabelledByElements (igc-input, igc-mask-input, igc-date-time-input)
• textarea: forward _internals.labels to the inner native <textarea>
• select, combo, date-picker, date-range-picker: forward _internals.labels to the inner input in updated(); date-range two-input mode targets the start input
• combo: add delegatesFocus so label activation focuses the inner input
• tests: add shared runExternalLabelAssociationTests covering IDREF and nested label association plus focus delegation

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

• My code follows the project's coding standards
• I have tested my changes locally

[Copilot]

Pull request overview

This PR improves accessibility and focus behavior for form-associated custom elements by forwarding external <label> associations (via for/id and label nesting) from the host element to the inner native control that assistive technologies expose.

Changes:

• Forward ElementInternals.labels from composite hosts (select/combo/date-picker/date-range-picker) to their inner input components, and bind ariaLabelledByElements on leaf native controls (input/mask-input/date-time-input/textarea).
• Enable delegatesFocus where needed so label activation results in correct focus delegation to the inner input.
• Add a shared test suite (runExternalLabelAssociationTests) and apply it across affected components; update changelog.

Reviewed changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/components/textarea/textarea.ts	Forwards associated external labels onto the native <textarea> via ariaLabelledByElements.
src/components/textarea/textarea.spec.ts	Adds shared external label association tests for textarea.
src/components/select/select.ts	Enables delegatesFocus and forwards host labels to inner igc-input.
src/components/select/select.spec.ts	Adds shared external label association tests for select.
src/components/mask-input/mask-input.ts	Applies resolved label elements to the masked native input template options.
src/components/mask-input/mask-input.spec.ts	Adds shared external label association tests for mask input.
src/components/input/input.ts	Applies resolved label elements to the native <input>.
src/components/input/input.spec.ts	Adds shared external label association tests for input.
src/components/input/input-base.ts	Introduces _labelElements forwarding state and _resolvedLabelElements resolution logic.
src/components/date-time-input/date-time-input.base.ts	Introduces _labelElements forwarding state and wires resolved labels into the native masked input.
src/components/date-time-input/date-time-input.spec.ts	Adds shared external label association tests for date-time input.
src/components/date-range-picker/date-range-picker.ts	Forwards host labels to the start input (single input mode or first input in two-input mode).
src/components/date-range-picker/date-range-picker-two-inputs.spec.ts	Adds shared external label association tests for two-input date range picker.
src/components/date-range-picker/date-range-picker-single.spec.ts	Adds shared external label association tests for single-input date range picker.
src/components/date-picker/date-picker.ts	Forwards host labels to the inner date-time input.
src/components/date-picker/date-picker.spec.ts	Adds shared external label association tests for date picker.
src/components/combo/combo.ts	Enables delegatesFocus and forwards host labels to the inner igc-input.
src/components/combo/combo.spec.ts	Adds shared external label association tests for combo.
src/components/common/utils.spec.ts	Adds the shared runExternalLabelAssociationTests test helper.
src/components/common/templates/masked-input.ts	Adds ariaLabelledByElements support to the shared masked input renderer.
src/components/common/mixins/forms/types.ts	Exposes _internals in typing for form-associated components.
src/components/common/mixins/forms/associated.ts	Renames internals controller field to protected _internals for subclass access.
src/components/common/controllers/internals.ts	Adds a labels getter to expose associated label elements.
CHANGELOG.md	Documents the new external label association behavior under Unreleased.