Fix the Syndication Feed RFC822 DateTimeParser (#99194)

* Fix the Syndication RFC822 DateTimeParser

RFC822 allows single-digit date values and two-digit year values in the publication date (pubDate). The existing date-time parser only accepted two-digit dates and (for some formats) four-digit years.

* Remove trailing whitespace in parseFormat array

Author: dougwaldron

src/libraries/System.ServiceModel.Syndication/src/System/ServiceModel/Syndication/DateTimeHelper.cs

@@ -92,28 +92,28 @@ private static bool Rfc822DateTimeParser(string dateTimeString, out DateTimeOffs
             DateTimeOffset theTime;
             string[] parseFormat =
             {
-                "ddd, dd MMMM yyyy HH:mm:ss zzz",
-                "dd MMMM yyyy HH:mm:ss zzz",
-                "ddd, dd MMM yyyy HH:mm:ss zzz",
-                "dd MMM yyyy HH:mm:ss zzz",
+                "ddd, d MMMM yyyy HH:mm:ss zzz",
+                "d MMMM yyyy HH:mm:ss zzz",
+                "ddd, d MMM yyyy HH:mm:ss zzz",
+                "d MMM yyyy HH:mm:ss zzz",
 
-                "ddd, dd MMMM yyyy HH:mm zzz",
-                "dd MMMM yyyy HH:mm zzz",
-                "ddd, dd MMM yyyy HH:mm zzz",
-                "dd MMM yyyy HH:mm zzz",
+                "ddd, d MMMM yyyy HH:mm zzz",
+                "d MMMM yyyy HH:mm zzz",
+                "ddd, d MMM yyyy HH:mm zzz",
+                "d MMM yyyy HH:mm zzz",
 
                 // The original RFC822 spec listed 2 digit years. RFC1123 updated the format to include 4 digit years and states that you should use 4 digits.
                 // Technically RSS2.0 specifies RFC822 but it's presumed that RFC1123 will be used as we're now past Y2K and everyone knows better. The 4 digit
                 // formats are listed first for performance reasons as it's presumed they will be more likely to match first.
-                "ddd, dd MMMM yy HH:mm:ss zzz",
-                "dd MMMM yyyy HH:mm:ss zzz",
-                "ddd, dd MMM yy HH:mm:ss zzz",
-                "dd MMM yyyy HH:mm:ss zzz",
-
-                "ddd, dd MMMM yy HH:mm zzz",
-                "dd MMMM yyyy HH:mm zzz",
-                "ddd, dd MMM yy HH:mm zzz",
-                "dd MMM yyyy HH:mm zzz"
+                "ddd, d MMMM yy HH:mm:ss zzz",
+                "d MMMM yy HH:mm:ss zzz",
+                "ddd, d MMM yy HH:mm:ss zzz",
+                "d MMM yy HH:mm:ss zzz",
+
+                "ddd, d MMMM yy HH:mm zzz",
+                "d MMMM yy HH:mm zzz",
+                "ddd, d MMM yy HH:mm zzz",
+                "d MMM yy HH:mm zzz"
             };
 
             if (DateTimeOffset.TryParseExact(wellFormattedString, parseFormat,