Sgen: Update GetTempAssemblyName according to #46499 (#57026)
* Update GetTempAssemblyName according to #46499
In #46499 we corrected Compilation.GetTempAssemblyName in order for it to be not deterministic under .NET Core.
In this PR we update the generated filename to match the new logic.
* Update Microsoft.XmlSerializer.Generator.csproj
* Update SGen.cs
Avoid using external dependency
* Update Microsoft.XmlSerializer.Generator.csproj
Avoid using external dependency
* Update Sgen.cs
Fixed compilation