Update IPDF_JSPLATFORM::m_pFormFillinfo comment.

Change-Id: I19b3422b624c8d31c35b680b444a5caf679a5aab
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/93451
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Auto-Submit: Tom Sepez <tsepez@chromium.org>
diff --git a/public/fpdf_formfill.h b/public/fpdf_formfill.h
index 0cafb9a..5393a03 100644
--- a/public/fpdf_formfill.h
+++ b/public/fpdf_formfill.h
@@ -307,7 +307,9 @@
                       int length);
 
   /*
-   * Pointer to FPDF_FORMFILLINFO interface.
+   * Pointer for embedder-specific data. Unused by PDFium, and despite
+   * its name, can be any data the embedder desires, though traditionally
+   * a FPDF_FORMFILLINFO interface.
    */
   void* m_pFormfillinfo;