Update Process.StartInfo to show exception thrown if Process.Start was not used (#2718)

* Update Process.StartInfo to show exception thrown if Process.Start was not used

* Fix XML

* Clarify

Author: danmoseley

xml/System.Diagnostics/Process.xml

@@ -5218,7 +5218,7 @@ There is a similar issue when you read all text from both the standard output an
 
  You can change the parameters specified in the <xref:System.Diagnostics.Process.StartInfo%2A> property up to the time that you call the <xref:System.Diagnostics.Process.Start%2A> method on the process. After you start the process, changing the <xref:System.Diagnostics.Process.StartInfo%2A> values does not affect or restart the associated process. If you call the <xref:System.Diagnostics.Process.Start%28System.Diagnostics.ProcessStartInfo%29> method with the <xref:System.Diagnostics.ProcessStartInfo.UserName%2A?displayProperty=nameWithType> and <xref:System.Diagnostics.ProcessStartInfo.Password%2A?displayProperty=nameWithType> properties set, the unmanaged `CreateProcessWithLogonW` function is called, which starts the process in a new window even if the <xref:System.Diagnostics.ProcessStartInfo.CreateNoWindow%2A> property value is `true` or the <xref:System.Diagnostics.ProcessStartInfo.WindowStyle%2A> property value is <xref:System.Diagnostics.ProcessWindowStyle.Hidden>.  
 
- If you did not use the <xref:System.Diagnostics.Process.Start%2A> method to start a process, the <xref:System.Diagnostics.Process.StartInfo%2A> property does not reflect the parameters used to start the process. For example, if you use <xref:System.Diagnostics.Process.GetProcesses%2A> to get an array of processes running on the computer, the <xref:System.Diagnostics.Process.StartInfo%2A> property of each <xref:System.Diagnostics.Process> does not contain the original file name or arguments used to start the process.  
+ You should only access the <xref:System.Diagnostics.Process.StartInfo%2A> property on a <xref:System.Diagnostics.Process> object returned by the <xref:System.Diagnostics.Process.Start%2A> method. For example, you should not access the <xref:System.Diagnostics.Process.StartInfo%2A> property on a <xref:System.Diagnostics.Process> object returned by <xref:System.Diagnostics.Process.GetProcesses%2A>. Otherwise, on .NET Core the <xref:System.Diagnostics.Process.StartInfo%2A> property will throw an <xref:System.InvalidOperationException> and on .NET Framework it will return a dummy <xref:System.Diagnostics.ProcessStartInfo> object.
 
  When the process is started, the file name is the file that populates the (read-only) <xref:System.Diagnostics.Process.MainModule%2A> property. If you want to retrieve the executable file that is associated with the process after the process has started, use the <xref:System.Diagnostics.Process.MainModule%2A> property. If you want to set the executable file of a <xref:System.Diagnostics.Process> instance for which an associated process has not been started, use the <xref:System.Diagnostics.Process.StartInfo%2A> property's <xref:System.Diagnostics.ProcessStartInfo.FileName%2A> member. Because the members of the <xref:System.Diagnostics.Process.StartInfo%2A> property are arguments that are passed to the <xref:System.Diagnostics.Process.Start%2A> method of a process, changing the <xref:System.Diagnostics.ProcessStartInfo.FileName%2A> property after the associated process has started will not reset the <xref:System.Diagnostics.Process.MainModule%2A> property. These properties are used only to initialize the associated process.  
 
@@ -5234,6 +5234,7 @@ There is a similar issue when you read all text from both the standard output an
  ]]></format>
         </remarks>
         <exception cref="T:System.ArgumentNullException">The value that specifies the <see cref="P:System.Diagnostics.Process.StartInfo" /> is <see langword="null" />.</exception>
+        <exception cref="T:System.InvalidOperationException">The <see cref="M:System.Diagnostics.Process.Start" /> method was not used to start the process.</exception>
         <permission cref="F:System.Security.Permissions.SecurityAction.LinkDemand">for full trust for the immediate caller. This member cannot be used by partially trusted code.</permission>
         <altmember cref="M:System.Diagnostics.Process.Start" />
         <altmember cref="P:System.Diagnostics.ProcessStartInfo.FileName" />