[Performance] XmlSerializationWriter.WriteTypedPrimitive is converting primitive types to string before writing them to the XmlWriter

[TrayanZapryanov]

Description

Possible optimization found.
Current implementation of writing primitive types fallbacks to string using XmlConvert.ToString(..).

runtime/src/libraries/System.Private.Xml/src/System/Xml/Serialization/XmlSerializationWriter.cs

Line 247 in 5c8aade

protected void WriteTypedPrimitive(string? name, string? ns, object o, bool xsiType)

Regression?

No

Analysis

How to optimize:
Write to char[] and then use XmlWriter.WriteChars(...). This should eliminate all temporary string for int/DateTime/guid.... types, which should be majority when serializing custom types. This change will help us later to use XmlSerializationWriter.WriteTypedPrimitive method in XmlSerializationWriterILGen instead of again creating strings and using XmlConvert.ToString(...)