fix(ui): strip row components from serializable form state

[rasitakyol]

What?

Remove row-level custom components when reducing admin form state to serializable fields.

Why?

Array and blocks rows can contain a React RowLabel component. That value may include circular references, so preview and SEO fields can fail while serializing form state even though top-level custom components are already removed.

How?

Clone and sanitize each row without mutating the original form state, while preserving row metadata such as IDs, block types, and collapsed state. A focused unit test covers circular row labels, top-level non-serializable values, preserved metadata, and input immutability.

Validation:

• pnpm test:unit packages/ui/src/forms/Form/reduceToSerializableFields.spec.ts
• pnpm eslint --max-warnings=0 packages/ui/src/forms/Form/reduceToSerializableFields.ts
• pnpm prettier --check packages/ui/src/forms/Form/reduceToSerializableFields.ts packages/ui/src/forms/Form/reduceToSerializableFields.spec.ts
• pnpm build:ui

Fixes #16786

[rasitakyol]

CI note after rebasing onto current main to trigger the previously approval-blocked full workflow: build, lint, and all completed non-Lexical checks are passing.

The failing LexicalHeadingFeature job failed during Payload initialization with the same transient MongoDB catalog-change error (payload._array-fields_versions, payloadInitError: true). The editor was then absent on every retry, before the suite logic could exercise this serializable-form-state patch. The same initialization signature is occurring concurrently across #17354, #17355, #17371, and #17372, whose diffs are unrelated.

No patch change is indicated by these logs. Some long-running Lexical jobs are still in progress; once they finish, a maintainer rerun of the failed E2E jobs would be appreciated.