AK: Add a basic formatter for wchar_t

Author: https://github.com/timschumi
Commit: 67a579aab0
Pull-request: https://github.com/SerenityOS/serenity/pull/10170
Reviewed-by: https://github.com/BertalanD ✅
Reviewed-by: https://github.com/Hendiadyoin1
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/kleinesfilmroellchen

Tests/AK/TestFormat.cpp

@@ -323,3 +323,17 @@ TEST_CASE(vector_format)
         EXPECT_EQ(String::formatted("{}", v), "[ [ 1, 2 ], [ 3, 4 ] ]");
     }
 }
+
+TEST_CASE(format_wchar)
+{
+    EXPECT_EQ(String::formatted("{}", L'a'), "a");
+    EXPECT_EQ(String::formatted("{}", L'\U0001F41E'), "\xF0\x9F\x90\x9E");
+    EXPECT_EQ(String::formatted("{:x}", L'a'), "61");
+    EXPECT_EQ(String::formatted("{:x}", L'\U0001F41E'), "1f41e");
+    EXPECT_EQ(String::formatted("{:d}", L'a'), "97");
+    EXPECT_EQ(String::formatted("{:d}", L'\U0001F41E'), "128030");
+
+    EXPECT_EQ(String::formatted("{:6}", L'a'), "a     ");
+    EXPECT_EQ(String::formatted("{:6d}", L'a'), "    97");
+    EXPECT_EQ(String::formatted("{:#x}", L'\U0001F41E'), "0x1f41e");
+}