AK: Define a formatter for char16_t

Author: https://github.com/trflynn89
Commit: b6dc5050d2
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5228
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/shannonbooth

AK/Format.cpp

@@ -990,6 +990,21 @@ ErrorOr<void> Formatter<char>::format(FormatBuilder& builder, char value)
         return formatter.format(builder, { &value, 1 });
     }
 }
+
+ErrorOr<void> Formatter<char16_t>::format(FormatBuilder& builder, char16_t value)
+{
+    if (m_mode == Mode::Binary || m_mode == Mode::BinaryUppercase || m_mode == Mode::Decimal || m_mode == Mode::Octal || m_mode == Mode::Hexadecimal || m_mode == Mode::HexadecimalUppercase) {
+        Formatter<u16> formatter { *this };
+        return formatter.format(builder, value);
+    } else {
+        StringBuilder codepoint;
+        codepoint.append_code_point(value);
+
+        Formatter<StringView> formatter { *this };
+        return formatter.format(builder, codepoint.string_view());
+    }
+}
+
 ErrorOr<void> Formatter<char32_t>::format(FormatBuilder& builder, char32_t value)
 {
     if (m_mode == Mode::Binary || m_mode == Mode::BinaryUppercase || m_mode == Mode::Decimal || m_mode == Mode::Octal || m_mode == Mode::Hexadecimal || m_mode == Mode::HexadecimalUppercase) {
@@ -1003,6 +1018,7 @@ ErrorOr<void> Formatter<char32_t>::format(FormatBuilder& builder, char32_t value
         return formatter.format(builder, codepoint.string_view());
     }
 }
+
 ErrorOr<void> Formatter<bool>::format(FormatBuilder& builder, bool value)
 {
     if (m_mode == Mode::Binary || m_mode == Mode::BinaryUppercase || m_mode == Mode::Decimal || m_mode == Mode::Octal || m_mode == Mode::Hexadecimal || m_mode == Mode::HexadecimalUppercase) {
@@ -1015,6 +1031,7 @@ ErrorOr<void> Formatter<bool>::format(FormatBuilder& builder, bool value)
         return formatter.format(builder, value ? "true"sv : "false"sv);
     }
 }
+
 ErrorOr<void> Formatter<long double>::format(FormatBuilder& builder, long double value)
 {
     u8 base;

AK/Format.h

@@ -547,8 +547,12 @@ struct Formatter<char> : StandardFormatter {
     ErrorOr<void> format(FormatBuilder&, char);
 };
 template<>
+struct Formatter<char16_t> : StandardFormatter {
+    ErrorOr<void> format(FormatBuilder&, char16_t);
+};
+template<>
 struct Formatter<char32_t> : StandardFormatter {
-    ErrorOr<void> format(FormatBuilder& builder, char32_t);
+    ErrorOr<void> format(FormatBuilder&, char32_t);
 };
 template<>
 struct Formatter<bool> : StandardFormatter {