Re-added DDS plugin support

Fork of [Qt 5.6 DDS plugin](https://code.qt.io/cgit/qt/qtimageformats.git/tree/src/plugins/imageformats/dds/qddshandler.cpp?h=5.6) under LGPL2.1.

- Merged all files in dds_p.h and dds.cpp
- Added support for Qt 6 image allocation limit
- Added checks for null image and datastream errors
- The plugin is disabled by default

CCBUG: 380956

Closes: #12

README.md

@@ -28,6 +28,7 @@ The following image formats have read-only support:
 The following image formats have read and write support:
 
 - AV1 Image File Format (avif)
+- DirectDraw Surface (dds)
 - Encapsulated PostScript (eps)
 - High Efficiency Image File Format (heif)
 - JPEG XL (jxl)
@@ -51,6 +52,8 @@ better to submit the plugin directly to the Qt Project.
 
 ## Duplicated Plugins
 
+### The TGA plugin
+
 The TGA plugin supports more formats than Qt's own TGA plugin;
 specifically, the one provided here supports indexed, greyscale and RLE
 images (types 1-3 and 9-11), while Qt's plugin only supports type 2
@@ -61,6 +64,11 @@ licensing.  If anyone were willing to write fresh code to improve Qt's
 TGA plugin, it would allow the TGA plugin in this framework to be
 removed.
 
+### The DDS plugin
+
+The DDS plugin is a fork from Qt 5.6. It will be activated once the 
+security issues are resolved.
+
 ## License
 
 This framework is licensed under the
@@ -114,6 +122,7 @@ plugin ('n/a' means no limit, i.e. the limit depends on the format encoding).
 
 - ANI: n/a
 - AVIF: 32,768 x 32,768 pixels, in any case no larger than 256 megapixels
+- DDS: n/a
 - EXR: 300,000 x 300,000 pixels
 - HDR: n/a (large image)
 - HEIF: n/a
@@ -162,6 +171,11 @@ without using the ICC profile.
 JXR, PSD and SCT plugins natively support 4-channel CMYK images when compiled 
 with Qt 6.8+.
 
+### The DDS plugin
+
+**This plugin is disabled by default. It can be enabled with the 
+`KIMAGEFORMATS_DDS` build option in the cmake file.**
+
 ### The HEIF plugin
 
 **This plugin is disabled by default. It can be enabled with the