AK: Add StringView::split_view() taking a StringView

Since the task of splitting a string via another is pretty common, we
might as well have this overload of split_view() as well.

AK/StringView.cpp

@@ -75,6 +75,32 @@ Vector<StringView> StringView::split_view(const char separator, bool keep_empty)
     return v;
 }
 
+Vector<StringView> StringView::split_view(const StringView& separator, bool keep_empty) const
+{
+    ASSERT(!separator.is_empty());
+
+    if (is_empty())
+        return {};
+
+    StringView view { *this };
+
+    Vector<StringView> parts;
+
+    auto maybe_separator_index = find_first_of(separator);
+    while (maybe_separator_index.has_value()) {
+        auto separator_index = maybe_separator_index.value();
+        auto part_with_separator = view.substring_view(0, separator_index + separator.length());
+        if (keep_empty || separator_index > 0)
+            parts.append(part_with_separator.substring_view(0, separator_index));
+        view = view.substring_view_starting_after_substring(part_with_separator);
+        maybe_separator_index = view.find_first_of(separator);
+    }
+    if (keep_empty || !view.is_empty())
+        parts.append(view);
+
+    return parts;
+}
+
 Vector<StringView> StringView::lines(bool consider_cr) const
 {
     if (is_empty())
@@ -244,7 +270,7 @@ Optional<size_t> StringView::find_first_of(const StringView& view) const
 
 Optional<size_t> StringView::find_last_of(char c) const
 {
-    for (size_t pos = m_length; --pos >0;) {
+    for (size_t pos = m_length; --pos > 0;) {
         if (m_characters[pos] == c)
             return pos;
     }

AK/StringView.h

@@ -88,6 +88,7 @@ public:
 
     StringView substring_view(size_t start, size_t length) const;
     Vector<StringView> split_view(char, bool keep_empty = false) const;
+    Vector<StringView> split_view(const StringView&, bool keep_empty = false) const;
 
     // Create a Vector of StringViews split by line endings. As of CommonMark
     // 0.29, the spec defines a line ending as "a newline (U+000A), a carriage