Bug description

• CS8350 -

MessagePackWriter Write(in ReadOnlySequence) does not have scoped, prevents stackalloc usage without unsafe (turns the error into a warning)

Repro steps

Try to use MessagePackWriter Write(in ReadOnlySpan) with a stackallocated span

Expected behavior

This is acceptable

Actual behavior

This is not acceptable

• Version used:
• Runtime: .Net Framework v 4.7.2

Additional context

I had to write custom serializers in the first place because our messages are proto defined, even though we're using MessagePack for the transport in .Net clients