Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

AK/StringBuilder.h

@@ -9,7 +9,7 @@ namespace AK {
 class StringBuilder {
 public:
     explicit StringBuilder(ssize_t initial_capacity = 16);
-    ~StringBuilder() { }
+    ~StringBuilder() {}
 
     void append(const String&);
     void append(char);
@@ -30,4 +30,3 @@ private:
 }
 
 using AK::StringBuilder;
-