Improve performance of layoutMultilineText

[seibar]

What?

Addresses: #1202. Previously long strings (> 10k characters) took very long for this function to execute (> 30 seconds). With this fix, a 10k character string executes in less than 1 second.

Testing?

• Added a unit test
• Executed integration tests (and fixed an issue that test number 15 uncovered)
• A lot of testing using the scratchpad.

New Dependencies?

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.

[ahaganDEV]

I tried this change out in my own fork of this library and it does indeed fix the performance issues with the function.

[ej-shafran]

This is great! layoutMultilineText was causing me massive problems and I eventually had to write a version of it on my own. Your version seems to work just as well, though.

[flogy]

Works like a charm, would be awesome to get this merged!