AK: Add Formatter for Vector

For debugging purposes, it is very useful to look at a Vector in a
simple list representation. Therefore, the new Formatter for Vector
provides a string representation of the following form:

```
[ 1, 2, 3, 4, 5 ]
```

This requires the content type of Vector to be formattable with default
arguments.

The current implementation ignores width and precision, which may be
accounted for later or passed down to the content formatter.

AK/Format.h

@@ -30,6 +30,12 @@ struct Formatter {
     using __no_formatter_defined = void;
 };
 
+template<typename T, typename = void>
+inline constexpr bool HasFormatter = true;
+
+template<typename T>
+inline constexpr bool HasFormatter<T, typename Formatter<T>::__no_formatter_defined> = false;
+
 constexpr size_t max_format_arguments = 256;
 
 struct TypeErasedParameter {
@@ -314,6 +320,49 @@ struct Formatter<StringView> : StandardFormatter {
     void format(FormatBuilder&, StringView value);
 };
 
+template<typename T>
+requires(HasFormatter<T>) struct Formatter<Vector<T>> : StandardFormatter {
+
+    Formatter() = default;
+    explicit Formatter(StandardFormatter formatter)
+        : StandardFormatter(formatter)
+    {
+    }
+    void format(FormatBuilder& builder, Vector<T> value)
+    {
+        if (m_mode == Mode::Pointer) {
+            Formatter<FlatPtr> formatter { *this };
+            formatter.format(builder, reinterpret_cast<FlatPtr>(value.data()));
+            return;
+        }
+
+        if (m_sign_mode != FormatBuilder::SignMode::Default)
+            VERIFY_NOT_REACHED();
+        if (m_alternative_form)
+            VERIFY_NOT_REACHED();
+        if (m_zero_pad)
+            VERIFY_NOT_REACHED();
+        if (m_mode != Mode::Default)
+            VERIFY_NOT_REACHED();
+        if (m_width.has_value() && m_precision.has_value())
+            VERIFY_NOT_REACHED();
+
+        m_width = m_width.value_or(0);
+        m_precision = m_precision.value_or(NumericLimits<size_t>::max());
+
+        Formatter<T> content_fmt;
+        builder.put_literal("[ ");
+        bool first = true;
+        for (auto& content : value) {
+            if (!first)
+                builder.put_literal(", ");
+            first = false;
+            content_fmt.format(builder, content);
+        }
+        builder.put_literal(" ]");
+    }
+};
+
 template<>
 struct Formatter<ReadonlyBytes> : Formatter<StringView> {
     void format(FormatBuilder& builder, ReadonlyBytes const& value)
@@ -509,12 +558,6 @@ void critical_dmesgln(CheckedFormatString<Parameters...>&& fmt, const Parameters
 }
 #endif
 
-template<typename T, typename = void>
-inline constexpr bool HasFormatter = true;
-
-template<typename T>
-inline constexpr bool HasFormatter<T, typename Formatter<T>::__no_formatter_defined> = false;
-
 template<typename T>
 class FormatIfSupported {
 public: