Restore accessible AcroForm options and explicit field font sizes

[tevinch]

What kind of change does this PR introduce?

Fixes #1803. Tagged form widgets can now receive alternateName (/TU) and structParent through the public form methods. An explicitly supplied fontSize also applies when the field uses the default form font; omitting it preserves inherited appearance behavior.

The structure reference captures the widget's page when it is created. Otherwise, adding a later page before finalizing the structure writes an OBJR pointing to that later page. Tests cover this delayed finalization together with nested field membership, distinct structure parents, Unicode/empty names, and explicit zero sizing.

Validation

• yarn test --maxWorkers=4: 61 files, 536 tests passed. The unrestricted run timed out in four visual tests; the four-worker run kept the existing 8-second timeout.
• yarn lint, yarn build, yarn test:package, and formatting checks passed.
• A two-page generated form passed veraPDF 1.30.2's ua1 profile: 106 rules and 593 checks, zero failures. The same local workflow passed through a CommonJS esbuild bundle with registered standard-font metrics.
• Two programmatic fill/save/reopen cycles preserved values, both pages, original text, metadata and widget/structure references. This does not establish PDF/UA conformance after editing: the pypdf appearance-generation probe failed separate font validation. No AWS deployment or human screen-reader test was performed.

Reproduction, source patch, sample PDF and detailed validation limits.

Checklist

• Unit Tests
• Documentation
• Update CHANGELOG.md
• Ready to be merged after review

[blikblum]

Please resolve the conflicts