AK: Use size_t for the length of strings

Using int was a mistake. This patch changes String, StringImpl,
StringView and StringBuilder to use size_t instead of int for lengths.
Obviously a lot of code needs to change as a result of this.

Libraries/LibHTML/CSS/StyleResolver.cpp

@@ -100,17 +100,17 @@ static Vector<String> split_on_whitespace(const StringView& string)
         return {};
 
     Vector<String> v;
-    int substart = 0;
-    for (int i = 0; i < string.length(); ++i) {
+    size_t substart = 0;
+    for (size_t i = 0; i < string.length(); ++i) {
         char ch = string.characters_without_null_termination()[i];
         if (isspace(ch)) {
-            int sublen = i - substart;
+            size_t sublen = i - substart;
             if (sublen != 0)
                 v.append(string.substring_view(substart, sublen));
             substart = i + 1;
         }
     }
-    int taillen = string.length() - substart;
+    size_t taillen = string.length() - substart;
     if (taillen != 0)
         v.append(string.substring_view(substart, taillen));
     return v;

Libraries/LibHTML/DOMTreeModel.cpp

@@ -68,7 +68,7 @@ int DOMTreeModel::column_count(const GModelIndex&) const
 static String with_whitespace_collapsed(const StringView& string)
 {
     StringBuilder builder;
-    for (int i = 0; i < string.length(); ++i) {
+    for (size_t i = 0; i < string.length(); ++i) {
         if (isspace(string[i])) {
             builder.append(' ');
             while (i < string.length()) {

Libraries/LibHTML/Layout/LayoutText.cpp

@@ -20,7 +20,7 @@ LayoutText::~LayoutText()
 
 static bool is_all_whitespace(const String& string)
 {
-    for (int i = 0; i < string.length(); ++i) {
+    for (size_t i = 0; i < string.length(); ++i) {
         if (!isspace(string[i]))
             return false;
     }

Libraries/LibHTML/Parser/CSSParser.cpp

@@ -135,15 +135,15 @@ public:
 
     bool next_is(const char* str) const
     {
-        int len = strlen(str);
-        for (int i = 0; i < len; ++i) {
+        size_t len = strlen(str);
+        for (size_t i = 0; i < len; ++i) {
             if (peek(i) != str[i])
                 return false;
         }
         return true;
     }
 
-    char peek(int offset = 0) const
+    char peek(size_t offset = 0) const
     {
         if ((index + offset) < css.length())
             return css[index + offset];
@@ -169,7 +169,7 @@ public:
 
     bool consume_whitespace_or_comments()
     {
-        int original_index = index;
+        size_t original_index = index;
         bool in_comment = false;
         for (; index < css.length(); ++index) {
             char ch = peek();
@@ -582,7 +582,7 @@ private:
     CurrentRule current_rule;
     Vector<char> buffer;
 
-    int index = 0;
+    size_t index = 0;
 
     StringView css;
 };

Libraries/LibHTML/Parser/HTMLParser.cpp

@@ -129,8 +129,8 @@ static bool parse_html_document(const StringView& html, Document& document, Pare
         }
     };
 
-    for (int i = 0; i < html.length(); ++i) {
-        auto peek = [&](int offset) -> char {
+    for (size_t i = 0; i < html.length(); ++i) {
+        auto peek = [&](size_t offset) -> char {
             if (i + offset >= html.length())
                 return '\0';
             return html[i + offset];
@@ -356,7 +356,7 @@ RefPtr<Document> parse_html_document(const StringView& html, const URL& url)
 String escape_html_entities(const StringView& html)
 {
     StringBuilder builder;
-    for (int i = 0; i < html.length(); ++i) {
+    for (size_t i = 0; i < html.length(); ++i) {
         if (html[i] == '<')
             builder.append("&lt;");
         else if (html[i] == '>')