[Process] Start process as non-elevated user

### Background and motivation

Today I've been studying some MSFT source code and I got to the conclusion that we most likely need to add the ability to start process as non-elevated user when running as elevated user.

One way of doing that on Windows would be to use following sys-calls:
- https://learn.microsoft.com/en-us/windows/win32/api/winsafer/nf-winsafer-safercreatelevel
- https://learn.microsoft.com/en-us/windows/win32/api/winsafer/nf-winsafer-safercomputetokenfromlevel
- https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessasusera

### API Proposal

The proposal is to extend `ProcessStartInfo` with a new `StartNonElevated ` property that indicates the process should be started as non-elevated user.

```csharp
namespace System.Diagnostics;
{
public sealed class ProcessStartInfo
{
public bool StartNonElevated { get; set; }
}
}
```

Any feedback is welcome!