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')

Tests/LibWeb/TestHTMLTokenizer.cpp

@@ -234,7 +234,7 @@ TEST_CASE(regression)
     auto file_size = MUST(file->size());
     auto content = MUST(ByteBuffer::create_uninitialized(file_size));
     MUST(file->read_until_filled(content.bytes()));
-    DeprecatedString file_contents { content.bytes() };
+    ByteString file_contents { content.bytes() };
     auto tokens = run_tokenizer(file_contents);
     u32 hash = hash_tokens(tokens);
     EXPECT_EQ(hash, 3657343287u);