Add widthOfText function to PDFPage

[ATLCTO]

What?

Helper function to calculate the width of some text so I can tweak the font size slightly to get the text to fit.

Why?

I am re-creating a document and I don't have access to the exact some fonts so I need to tweak the font size slightly to get the same layout.

How?

It's essentially the drawText function (just without the drawing).

Testing?

It's just a few lines of code from drawText and we've been using in production for a year or two, just trying to cleanup my build scripts and contribute the code to a upstream fork that will be maintained.

New Dependencies?

None

Screenshots

N/A

Suggested Reading?

No

Anything Else?

None

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.