AK: Add StringView(String const&) constructor

This allows us to pass the new String type to functions that take a
StringView directly, having to call bytes_as_string_view() every time
gets old quickly.

AK/StringView.cpp

@@ -16,11 +16,18 @@
 #ifndef KERNEL
 #    include <AK/DeprecatedString.h>
 #    include <AK/FlyString.h>
+#    include <AK/String.h>
 #endif
 
 namespace AK {
 
 #ifndef KERNEL
+StringView::StringView(String const& string)
+    : m_characters(reinterpret_cast<char const*>(string.bytes().data()))
+    , m_length(string.bytes().size())
+{
+}
+
 StringView::StringView(DeprecatedString const& string)
     : m_characters(string.characters())
     , m_length(string.length())