fix: omit disabled options from multi-select changes - #14002

Proposed Changes

Disabled options remain in selectedOptions, so changing a multiple select currently includes disabled options and options inside disabled optgroups in the form value and submission. It also lets required pass when only disabled options remain selected.

Filter disabled options when reading the DOM selection, consistently with checkbox and radio groups. The optgroup check follows the full ancestor chain, while the optional method call preserves custom select refs without DOM methods. Explicit defaultValues and setValue assignments remain intact.

Regression coverage includes selection and submission, required validation, explicit value assignments, and custom select refs.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Test plan

• pnpm test --runInBand: 133 suites, 1,836 tests and 26 snapshots passed.
• pnpm build, pnpm type, pnpm test:type, and pnpm lint passed.
• Public createFormControl checks cover custom refs, dynamic disabled groups and explicit value assignments.
• Browser automation is checked by repository CI.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new lint warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes