Fix some typos in //public

Found by Tricium.

Change-Id: Ib9a89eda6197400e57eaeb56a70226b80dc4c2dc
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/120811
Reviewed-by: Thomas Sepez <tsepez@google.com>
Commit-Queue: Lei Zhang <thestig@chromium.org>

public/fpdf_formfill.h

diff --git a/public/fpdf_formfill.h b/public/fpdf_formfill.h
index 2e710c8..1f0b129 100644
--- a/public/fpdf_formfill.h
+++ b/public/fpdf_formfill.h
@@ -280,7 +280,7 @@
   // Return Value:
   //       Number of bytes the filePath consumes, including trailing zeros.
   // Comments:
-  //       The filePath shoule always be provided in local encoding.
+  //       The filePath should always be provided in local encoding.
   int (*Field_browse)(struct _IPDF_JsPlatform* pThis,
                       void* filePath,
                       int length);
@@ -1498,7 +1498,7 @@
                                                  FPDF_PAGE page);
 
 // Function: FORM_Undo
-//       Make the current focussed widget perform an undo operation.
+//       Make the current focused widget perform an undo operation.
 // Parameters:
 //       hHandle     -   Handle to the form fill module, as returned by
 //                       FPDFDOC_InitFormFillEnvironment().
@@ -1509,7 +1509,7 @@
                                               FPDF_PAGE page);
 
 // Function: FORM_Redo
-//       Make the current focussed widget perform a redo operation.
+//       Make the current focused widget perform a redo operation.
 // Parameters:
 //       hHandle     -   Handle to the form fill module, as returned by
 //                       FPDFDOC_InitFormFillEnvironment().

public/fpdf_sysfontinfo.h

diff --git a/public/fpdf_sysfontinfo.h b/public/fpdf_sysfontinfo.h
index 9152c88..83c583e 100644
--- a/public/fpdf_sysfontinfo.h
+++ b/public/fpdf_sysfontinfo.h
@@ -75,7 +75,7 @@
   // Return Value:
   //          None
   // Comments:
-  //          Implementations should call FPDF_AddIntalledFont() function for
+  //          Implementations should call FPDF_AddInstalledFont() function for
   //          each font found. Only TrueType/OpenType and Type1 fonts are
   //          accepted by PDFium.
   void (*EnumFonts)(struct _FPDF_SYSFONTINFO* pThis, void* pMapper);