exr: write support and more

- Added support for writing EXR files
- Large image support (tested with 32GiB 16-bit image)
- OpenEXR multithreaded read/write support through the use of line blocks
- Build option to enable conversion to sRGB when read (disabled by default)
- Multi-view image reading support
- Options support: Size, ImageFormat, Quality, CompressRatio
- Metadata write/read support via EXR attributes

The plugin is now quite complete. It should also work on KF5 (not tested): if there is the will to include this MR also on KF5, let me know and I will do all the necessary tests.

README.md

@@ -17,7 +17,6 @@ The following image formats have read-only support:
 - Camera RAW images (arw, cr2, cr3, dcs, dng, ...)
 - Gimp (xcf)
 - Krita (kra)
-- OpenEXR (exr)
 - OpenRaster (ora)
 - Photoshop documents (psd, psb, pdd, psdt)
 - Radiance HDR (hdr)
@@ -29,6 +28,7 @@ The following image formats have read and write support:
 - Encapsulated PostScript (eps)
 - High Efficiency Image File Format (heif). Can be enabled with the KIMAGEFORMATS_HEIF build option.
 - JPEG XL (jxl)
+- OpenEXR (exr)
 - Personal Computer Exchange (pcx)
 - Quite OK Image format (qoi)
 - SGI images (rgb, rgba, sgi, bw)
@@ -45,10 +45,6 @@ of Qt is the license.  As such, if you write an imageformat plugin and
 you are willing to sign the Qt Project contributor agreement, it may be
 better to submit the plugin directly to the Qt Project.
 
-Note that the imageformat plugins provided by this module also provide a
-desktop file.  This is for the benefit of KImageIO in the KDE4 Support
-framework.
-
 ## Duplicated Plugins
 
 The TGA plugin supports more formats than Qt's own TGA plugin;