[API Proposal]: Add ReadOnlySequence<char> overload for WriteRawValue

[Tragetaschen]

Background and motivation

In #68223, two overloads for Utf8JsonWriter were proposed, one for ReadOnlySequence<byte> and one for ReadOnlySequence<char>. The latter was rejected due to the necessary surrogate pair state handling while writing the ReadOnlySpan<char> segments.

However, #67337 is currently underway to add the building blocks and state handling for that. Adding the rejected overload now seems like an easy addition.

API Proposal

namespace System.Text.Json
{
    public sealed partial class Utf8JsonWriter
    {
+        public void WriteRawValue(ReadOnlySequence<char> json, bool skipInputValidation = false);
    }
}

API Usage

I could avoid building an entire in-memory, contiguous string just to have it written out as JSON. Other proposals like #97570 would tie in very nicely as well.

Alternative Designs

No response

Risks

No response

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