AK: Replace the mutable String::replace API with an immutable version

This removes the awkward String::replace API which was the only String
API which mutated the String and replaces it with a new immutable
version that returns a new String with the replacements applied. This
also fixes a couple of UAFs that were caused by the use of this API.

As an optimization an equivalent StringView::replace API was also added
to remove an unnecessary String allocations in the format of:
`String { view }.replace(...);`

AK/StringView.cpp

@@ -245,4 +245,9 @@ bool StringView::operator==(const String& string) const
 
 String StringView::to_string() const { return String { *this }; }
 
+String StringView::replace(const StringView& needle, const StringView& replacement, bool all_occurrences) const
+{
+    return StringUtils::replace(*this, needle, replacement, all_occurrences);
+}
+
 }