AK: Change some argument and return types in Utf8View from int to size_t

This changes the return type of Utf8View::byte_length and the argument
types of substring_view from int to size_t.

AK/Utf8View.cpp

@@ -53,7 +53,7 @@ size_t Utf8View::byte_offset_of(const Utf8CodepointIterator& it) const
     return it.m_ptr - begin_ptr();
 }
 
-Utf8View Utf8View::substring_view(int byte_offset, int byte_length) const
+Utf8View Utf8View::substring_view(size_t byte_offset, size_t byte_length) const
 {
     StringView string = m_string.substring_view(byte_offset, byte_length);
     return Utf8View { string };

AK/Utf8View.h

@@ -55,9 +55,9 @@ public:
     Utf8CodepointIterator end() const;
 
     const unsigned char* bytes() const { return begin_ptr(); }
-    int byte_length() const { return m_string.length(); }
+    size_t byte_length() const { return m_string.length(); }
     size_t byte_offset_of(const Utf8CodepointIterator&) const;
-    Utf8View substring_view(int byte_offset, int byte_length) const;
+    Utf8View substring_view(size_t byte_offset, size_t byte_length) const;
     bool is_empty() const { return m_string.is_empty(); }
 
     bool starts_with(const Utf8View&) const;