Use static DateTime.UnixEpoch and RandomNumberGenerator.Fill() (PowerShell#18621)

Author: turbedi

src/Microsoft.PowerShell.Commands.Utility/commands/utility/GetDateCommand.cs

@@ -376,8 +376,6 @@ protected override void ProcessRecord()
             }
         }
 
-        private static readonly DateTime s_epoch = new(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
-
         /// <summary>
         /// This is more an implementation of the UNIX strftime.
         /// </summary>
@@ -501,7 +499,7 @@ private string UFormatDateString(DateTime dateTime)
                             break;
 
                         case 's':
-                            sb.Append(StringUtil.Format("{0:0}", dateTime.ToUniversalTime().Subtract(s_epoch).TotalSeconds));
+                            sb.Append(StringUtil.Format("{0:0}", dateTime.ToUniversalTime().Subtract(DateTime.UnixEpoch).TotalSeconds));
                             break;
 
                         case 'T':

src/System.Management.Automation/engine/hostifaces/MshHostUserInterface.cs

@@ -1167,8 +1167,8 @@ internal static string GetTranscriptPath(string baseDirectory, bool includeDate)
             // bytes of randomness (2^48 = 2.8e14) would take an attacker about 891 years to guess
             // a filename (assuming they knew the time the transcript was started).
             // (5 bytes = 3 years, 4 bytes = about a month)
-            byte[] randomBytes = new byte[6];
-            System.Security.Cryptography.RandomNumberGenerator.Create().GetBytes(randomBytes);
+            Span<byte> randomBytes = stackalloc byte[6];
+            System.Security.Cryptography.RandomNumberGenerator.Fill(randomBytes);
             string filename = string.Format(
                         Globalization.CultureInfo.InvariantCulture,
                         "PowerShell_transcript.{0}.{1}.{2:yyyyMMddHHmmss}.txt",