AK: Prepare Utf32View for use within templated LibGfx contexts

Forward declare its iterator and add a peek() method analagous to
Utf8CodePointIterator::peek().

AK/Forward.h

@@ -44,6 +44,7 @@ class Time;
 class URL;
 class String;
 class Utf16View;
+class Utf32CodePointIterator;
 class Utf32View;
 class Utf8CodePointIterator;
 class Utf8View;
@@ -201,6 +202,7 @@ using AK::Time;
 using AK::Traits;
 using AK::URL;
 using AK::Utf16View;
+using AK::Utf32CodePointIterator;
 using AK::Utf32View;
 using AK::Utf8CodePointIterator;
 using AK::Utf8View;

AK/Utf32View.cpp

@@ -9,6 +9,24 @@
 
 namespace AK {
 
+Optional<u32> Utf32CodePointIterator::peek(size_t offset) const
+{
+    if (offset == 0) {
+        if (this->done())
+            return {};
+        return this->operator*();
+    }
+
+    auto new_iterator = *this;
+    for (size_t index = 0; index < offset; ++index) {
+        ++new_iterator;
+        if (new_iterator.done())
+            return {};
+    }
+
+    return *new_iterator;
+}
+
 ErrorOr<void> Formatter<Utf32View>::format(FormatBuilder& builder, Utf32View const& string)
 {
     return builder.builder().try_append(string);

AK/Utf32View.h

@@ -43,6 +43,9 @@ public:
         return *m_ptr;
     }
 
+    // NOTE: This returns {} if the peek is at or past EOF.
+    Optional<u32> peek(size_t offset = 0) const;
+
     constexpr int code_point_length_in_bytes() const { return sizeof(u32); }
     bool done() const { return !m_length; }