[API Proposal]: Add GetElapsedTime(long)

[tarekgh]

Background and motivation

We've added a useful feature called TimeProvider.GetElapsedTime(long startingTimestamp, long endingTimestamp). However, we've identified another frequently used scenario where users want to calculate the elapsed time from the starting timestamp to the current timestamp. To achieve this, users must currently call:

timeProvider.GetElapsedTime(startingTimestamp, timeProvider.GetTimestamp());

To simplify this process, we propose introducing an overload for GetElapsedTime that allows users to simply call timeProvider.GetElapsedTime(startingTimestamp) without having to manually call GetTimestamp() each time they want to calculate the elapsed time.

Also, will be consistent with Stopwatch.GetElapsedTime(system-int64)

API Proposal

namespace System
{
    public abstract class TimeProvider
    {
	    /// <summary>
	    /// Gets the elapsed time since the <paramref name="startingTimestamp"/> value retrieved using <see cref="GetTimestamp"/>.
	    /// </summary>
        public TimeSpan GetElapsedTime(long startingTimestamp)
    }
}

API Usage

long startingTimestamp = timeProvider.GetTimeStamp();

// .... do some work here

TimeSpan timeProvider.GetElapsedTime(startingTimestamp);

Alternative Designs

No response

Risks

No response

[tarekgh]

CC @sebastienros @stephentoub

[bartonjs]

Video

Looks good as proposed

namespace System
{
    public partial class TimeProvider
    {
	    /// <summary>
	    /// Gets the elapsed time since the <paramref name="startingTimestamp"/> value retrieved using <see cref="GetTimestamp"/>.
	    /// </summary>
        public TimeSpan GetElapsedTime(long startingTimestamp)
    }
}