LibGfx/TIFF: Add support for the IFD type

As described in the first edition of the TIFF technical notes, the IFD
type is identical to Long (UnsignedLong) except that it only contains
offset of valid IFDs.

https://www.awaresystems.be/imaging/tiff/specification/TIFFPM6.pdf

Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.cpp

@@ -468,6 +468,7 @@ private:
         }
         case Type::UnsignedShort:
             return read_every_values.template operator()<u16>();
+        case Type::IFD:
         case Type::UnsignedLong:
             return read_every_values.template operator()<u32>();
         case Type::UnsignedRational:

Userland/Libraries/LibGfx/ImageFormats/TIFFLoader.h

@@ -11,8 +11,12 @@
 
 namespace Gfx {
 
+// This is a link to the main TIFF specification from 1992
 // https://www.itu.int/itudoc/itu-t/com16/tiff-fx/docs/tiff6.pdf
 
+// First TIFF Technical notes from 1995
+// https://www.awaresystems.be/imaging/tiff/specification/TIFFPM6.pdf
+
 namespace TIFF {
 class TIFFLoadingContext;
 }

Userland/Libraries/LibGfx/TIFFGenerator.py

@@ -40,6 +40,7 @@ class TIFFType(EnumWithExportName):
     SignedRational = 10, 8
     Float = 11, 4
     Double = 12, 8
+    IFD = 13, 4
     UTF8 = 129, 1
 
 
@@ -218,7 +219,7 @@ def tiff_type_to_cpp(t: TIFFType, with_promotion: bool = True) -> str:
         return 'ByteBuffer'
     if t == TIFFType.UnsignedShort:
         return 'u16'
-    if t == TIFFType.UnsignedLong:
+    if t == TIFFType.UnsignedLong or t == TIFFType.IFD:
         return 'u32'
     if t == TIFFType.UnsignedRational:
         return 'TIFF::Rational<u32>'