gdk-pixbuf: add .clang-format

Plug-ins from https://gitlab.gnome.org/GNOME/gdk-pixbuf/
use similar coding style.

contrib/gdk-pixbuf/.clang-format

@@ -0,0 +1,23 @@
+# Coding style is similar to https://gitlab.gnome.org/GNOME/gdk-pixbuf/
+# IndentWidth is reduced to 4 instead of 8.
+Language: Cpp
+BasedOnStyle: GNU
+IndentWidth: 4
+AlwaysBreakAfterDefinitionReturnType: All
+BreakBeforeBinaryOperators: true
+BinPackParameters: false
+SpaceAfterCStyleCast: true
+IndentCaseLabels: false
+IndentCaseBlocks: false
+BreakBeforeBraces: Custom
+AlignAfterOpenBracket: Align
+BraceWrapping:
+  AfterCaseLabel: false
+  AfterEnum: true
+  AfterFunction: true
+  AfterStruct: true
+  AfterUnion: true
+  BeforeElse: false
+  BeforeWhile: false
+  IndentBraces: false
+ColumnLimit: 0