AnyImageConverter: recognize KTX2 files.

Preparing for the soon-to-be-merged KTX files. Not hooking up 1D/3D and
the compressed APIs yet, doing that only when the plugins get merged so
I have a way to test.

src/MagnumPlugins/AnyImageConverter/AnyImageConverter.cpp

@@ -92,6 +92,8 @@ bool AnyImageConverter::doConvertToFile(const ImageView2D& image, const Containe
             normalized.hasSuffix(".jpeg"_s) ||
             normalized.hasSuffix(".jpe"_s))
         plugin = "JpegImageConverter"_s;
+    else if(normalized.hasSuffix(".ktx2"_s))
+        plugin = "KtxImageConverter"_s;
     else if(normalized.hasSuffix(".png"_s))
         plugin = "PngImageConverter"_s;
     else if(normalized.hasSuffix(".tga"_s) ||

src/MagnumPlugins/AnyImageConverter/AnyImageConverter.h

@@ -66,6 +66,8 @@ tries to convert the file with it. Supported formats for uncompressed data:
     `HdrImageConverter`
 -   JPEG (`*.jpg`, `*.jpe`, `*.jpeg`), converted with @ref JpegImageConverter
     or any other plugin that provides it
+-   KTX2 (`*.ktx2`), converted with any plugin that provides
+    `KtxImageConverter`
 -   Portable Network Graphics (`*.png`), converted with @ref PngImageConverter
     or any other plugin that provides it
 -   Truevision TGA (`*.tga`, `*.vda`, `*.icb`, `*.vst`), converted with

src/MagnumPlugins/AnyImageConverter/Test/AnyImageConverterTest.cpp

@@ -153,6 +153,7 @@ constexpr struct {
     {"JPEG", "file.jpg", "JpegImageConverter"},
     {"JPEG weird extension", "file.jpe", "JpegImageConverter"},
     {"JPEG uppercase", "output.JPG", "JpegImageConverter"},
+    {"KTX2", "foo.ktx2", "KtxImageConverter"},
     {"PNG", "file.png", "PngImageConverter"}
 };