PDFForm.flatten() does not handle rotated fields correctly

[Hopding]

PDF form fields can be rotated. However, the rotation logic for form field widgets should be "in-place" (see rotateInPlace), as opposed to the more common (at least in PDF land) logic of "about-the-origin" rotation. The current logic used in PDFForm.flatten() appears to be using "about-the-origin" logic, which leads to incorrect results after flattening a rotated field. See below for examples clarifying this:

✅ Correct Rendering of Rotated Fields

You can generate this document yourself by running yarn apps:node 17 and looking at the first page of the resulting document.

❌ Incorrect Rendering of Rotated Fields

You can generate this document yourself by running yarn apps:node 18 and looking at the fifth page of the resulting document.

[Hopding]

@btecu Think it would be fairly straightforward to use rotateInPlace for flattening? I'm assuming that's not what's currently being used.

[btecu]

Curiously, this evening it was brought to my attention this issue so it was already on my radar.
The document before the fix:

After the fix:

I've also tested the document mentioned above and it's also fixed.

[princ09]

Hi @Hopding , Thanks for this wonderful lib. I just saw documentation related rotateInPlace but I am not able to understand how to use it. should be used with PngImage?
I want to have like this https://user-images.githubusercontent.com/47990313/103611620-ab976f00-4f48-11eb-9eb6-c37802238308.jpg
where pdf might be rotated but image i want to be fixed at top left.
Please provide example for rotateInPlace for pngImage.