Add new era in Japan called "Reiwa"

src/System.Private.CoreLib/shared/System/Globalization/JapaneseCalendar.cs

@@ -14,11 +14,11 @@ namespace System.Globalization
     /// and the era begins on the day an emperor ascends the throne and continues until his death.
     /// The era changes at 12:00AM.
     ///
-    /// For example, the current era is Heisei.  It started on 1989/1/8 A.D.  Therefore, Gregorian year 1989 is also Heisei 1st.
-    /// 1989/1/8 A.D. is also Heisei 1st 1/8.
+    /// For example, the current era is Reiwa.  It started on 2019/5/1 A.D.  Therefore, Gregorian year 2019 is also Reiwa 1st.
+    /// 2019/5/1 A.D. is also Reiwa 1st 5/1.
     ///
     /// Any date in the year during which era is changed can be reckoned in either era.  For example,
-    /// 1989/1/1 can be 1/1 Heisei 1st year or 1/1 Showa 64th year.
+    /// 2019/1/1 can be 1/1 Reiwa 1st year or 1/1 Heisei 31st year.
     ///
     /// Note:
     ///  The DateTime can be represented by the JapaneseCalendar are limited to two factors:
@@ -30,7 +30,7 @@ namespace System.Globalization
     ///     Calendar    Minimum     Maximum
     ///     ==========  ==========  ==========
     ///     Gregorian   1868/09/08  9999/12/31
-    ///     Japanese    Meiji 01/01 Heisei 8011/12/31
+    ///     Japanese    Meiji 01/01 Reiwa 7981/12/31
     /// </remarks>
     public partial class JapaneseCalendar : Calendar
     {
@@ -74,7 +74,8 @@ internal static EraInfo[] GetEraInfo()
                 // See if we have to use the built-in eras
                 (s_japaneseEraInfo = new EraInfo[]
                 {
-                    new EraInfo(4, 1989, 1, 8, 1988, 1, GregorianCalendar.MaxYear - 1988, "\x5e73\x6210", "\x5e73", "H"),
+                    new EraInfo(5, 2019, 5, 1, 2018, 1, GregorianCalendar.MaxYear - 2018, "\x4ee4\x548c", "\x4ee4", "R"),
+                    new EraInfo(4, 1989, 1, 8, 1988, 1, 2019 - 1988, "\x5e73\x6210", "\x5e73", "H"),
                     new EraInfo(3, 1926, 12, 25, 1925, 1, 1989 - 1925, "\x662d\x548c", "\x662d", "S"),
                     new EraInfo(2, 1912, 7, 30, 1911, 1, 1926 - 1911, "\x5927\x6b63", "\x5927", "T"),
                     new EraInfo(1, 1868, 1, 1, 1867, 1, 1912 - 1867, "\x660e\x6cbb", "\x660e", "M")