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/LibGfx/ImageFormats/ImageDecoder.cpp

@@ -86,7 +86,7 @@ static OwnPtr<ImageDecoderPlugin> probe_and_sniff_for_appropriate_plugin_with_kn
     return {};
 }
 
-RefPtr<ImageDecoder> ImageDecoder::try_create_for_raw_bytes(ReadonlyBytes bytes, Optional<DeprecatedString> mime_type)
+RefPtr<ImageDecoder> ImageDecoder::try_create_for_raw_bytes(ReadonlyBytes bytes, Optional<ByteString> mime_type)
 {
     if (OwnPtr<ImageDecoderPlugin> plugin = probe_and_sniff_for_appropriate_plugin(bytes); plugin)
         return adopt_ref_if_nonnull(new (nothrow) ImageDecoder(plugin.release_nonnull()));