Everywhere: Rename {Deprecated => Byte}String

This commit un-deprecates DeprecatedString, and repurposes it as a byte
string.
As the null state has already been removed, there are no other
particularly hairy blockers in repurposing this type as a byte string
(what it _really_ is).

This commit is auto-generated:
  $ xs=$(ack -l \bDeprecatedString\b\|deprecated_string AK Userland \
    Meta Ports Ladybird Tests Kernel)
  $ perl -pie 's/\bDeprecatedString\b/ByteString/g;
    s/deprecated_string/byte_string/g' $xs
  $ clang-format --style=file -i \
    $(git diff --name-only | grep \.cpp\|\.h)
  $ gn format $(git ls-files '*.gn' '*.gni')

Userland/Libraries/LibWeb/HTML/HTMLOutputElement.h

@@ -23,9 +23,9 @@ class HTMLOutputElement final
 public:
     virtual ~HTMLOutputElement() override;
 
-    DeprecatedString const& type() const
+    ByteString const& type() const
     {
-        static DeprecatedString output = "output";
+        static ByteString output = "output";
         return output;
     }