Set page reference for new field Widgets

[Trapfether]

What?

Sets the page reference for field widgets when they are added to a page

Why?

Currently the library does not set the page reference, causing code intended to find the widget's page to fail. Notably, some internal code is also tripped up by this currently as it uses the same methodology.

Ex:
`

const pages = PDFDoc.getPages();
const field = PDFField;
const widget = field.getWidgets()[0];
const pageIndex = pages.findIndex(function(x){return x.ref === widget.P()});
const page = pages[pageIndex];

`

How?

A function has been added to PDFField updateWidgetPageReference that takes the widget annotation and the PDFRef for the page and adds that reference to the widget's dictionary.

This function is called at the end of a fields addToPage function just after adding the widget annotation to the page's internal node

Testing?

I added a unit test for each field that supports an addToPage function. Upon making my changes, I verified that those tests now passed. I also checked the Integration tests to be sure nothing there was messed up. Everything appeared to be in order.

New Dependencies?

No

Screenshots

N/A

Suggested Reading?

Partly

Anything Else?

Linter found a lint rule violation in the src/api/index.ts file. I did not push that as it was unrelated to this fix

Checklist

• I read CONTRIBUTING.md.
• I read MAINTAINERSHIP.md#pull-requests.
• I added/updated unit tests for my changes.
• I added/updated integration tests for my changes.
• I ran the integration tests.
• I tested my changes in Node, Deno, and the browser.
• I viewed documents produced with my changes in Adobe Acrobat, Foxit Reader, Firefox, and Chrome.
• I added/updated doc comments for any new/modified public APIs.
• My changes work for both new and existing PDF files.
• I ran the linter on my changes.

[Hopding]

Looks great overall! Just requested a small refactor.