AK: Make Default be the default formatting mode for Bytes

There is no way to opt out of the HexDump formatting mode. So let's use
the default `Span` formatter and allow the user to opt in the HexDump
mode for `Span<u8>` aka `Bytes`.

This is mainly useful to print `Vector<u8>`, as the `Vector` formatter
is implemented on top of the `Span` formatter.

AK/Format.h

@@ -438,13 +438,7 @@ struct Formatter<StringView> : StandardFormatter {
 
 template<typename T>
 requires(HasFormatter<T>)
-struct Formatter<ReadonlySpan<T>> : StandardFormatter {
-    Formatter() = default;
-    explicit Formatter(StandardFormatter formatter)
-        : StandardFormatter(move(formatter))
-    {
-    }
-
+struct Formatter<ReadonlySpan<T>> : Formatter<StringView> {
     ErrorOr<void> format(FormatBuilder& builder, ReadonlySpan<T> value)
     {
         if (m_mode == Mode::Pointer) {
@@ -453,6 +447,11 @@ struct Formatter<ReadonlySpan<T>> : StandardFormatter {
             return {};
         }
 
+        if constexpr (IsSame<T, u8>) {
+            if (m_mode == Mode::HexDump)
+                return Formatter<StringView>::format(builder, value);
+        }
+
         if (m_sign_mode != FormatBuilder::SignMode::Default)
             VERIFY_NOT_REACHED();
         if (m_alternative_form)
@@ -501,26 +500,6 @@ struct Formatter<Vector<T, inline_capacity>> : Formatter<ReadonlySpan<T>> {
     }
 };
 
-template<>
-struct Formatter<ReadonlyBytes> : Formatter<StringView> {
-    ErrorOr<void> format(FormatBuilder& builder, ReadonlyBytes value)
-    {
-        if (m_mode == Mode::Pointer) {
-            Formatter<FlatPtr> formatter { *this };
-            return formatter.format(builder, reinterpret_cast<FlatPtr>(value.data()));
-        }
-        if (m_mode == Mode::Default || m_mode == Mode::HexDump) {
-            m_mode = Mode::HexDump;
-            return Formatter<StringView>::format(builder, value);
-        }
-        return Formatter<StringView>::format(builder, value);
-    }
-};
-
-template<>
-struct Formatter<Bytes> : Formatter<ReadonlyBytes> {
-};
-
 // FIXME: Printing raw char pointers is inherently dangerous. Remove this and
 //        its users and prefer StringView over it.
 template<>

Tests/AK/TestFormat.cpp

@@ -397,6 +397,18 @@ TEST_CASE(vector_format)
     }
 }
 
+TEST_CASE(read_only_bytes_format)
+{
+    {
+        Vector<u8> v { 1, 2, 3, 4 };
+        EXPECT_EQ(ByteString::formatted("{}", v), "[ 1, 2, 3, 4 ]");
+    }
+    {
+        Vector<u8> v { 1, 2, 3, 4 };
+        EXPECT_EQ(ByteString::formatted("{:hex-dump}", v), "01020304");
+    }
+}
+
 TEST_CASE(format_wchar)
 {
     EXPECT_EQ(ByteString::formatted("{}", L'a'), "a");