Fix TimeZone Names (#106056)

Author: tarekgh

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

@@ -220,6 +220,10 @@ public AdjustmentRule[] GetAdjustmentRules()
             return rulesList.ToArray();
         }
 
+        private string NameLookupId =>
+                HasIanaId ? Id :
+                (_equivalentZones is not null && _equivalentZones.Count > 0 ? _equivalentZones[0].Id : (GetAlternativeId(Id, out _) ?? Id));
+
         private string? PopulateDisplayName()
         {
             if (IsUtcAlias(Id))
@@ -231,7 +235,7 @@ public AdjustmentRule[] GetAdjustmentRules()
             if (GlobalizationMode.Invariant)
                 return displayName;
 
-            GetFullValueForDisplayNameField(Id, BaseUtcOffset, ref displayName);
+            GetFullValueForDisplayNameField(NameLookupId, BaseUtcOffset, ref displayName);
 
             return displayName;
         }
@@ -245,7 +249,7 @@ public AdjustmentRule[] GetAdjustmentRules()
             if (GlobalizationMode.Invariant)
                 return standardDisplayName;
 
-            GetStandardDisplayName(Id, ref standardDisplayName);
+            GetStandardDisplayName(NameLookupId, ref standardDisplayName);
 
             return standardDisplayName;
         }
@@ -259,7 +263,7 @@ public AdjustmentRule[] GetAdjustmentRules()
             if (GlobalizationMode.Invariant)
                 return daylightDisplayName;
 
-            GetDaylightDisplayName(Id, ref daylightDisplayName);
+            GetDaylightDisplayName(NameLookupId, ref daylightDisplayName);
 
             return daylightDisplayName;
         }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -3211,6 +3211,32 @@ public static void TestCustomTimeZonesWithNullNames()
             Assert.Equal(string.Empty, custom.DisplayName);
         }
 
+        [InlineData("Eastern Standard Time", "America/New_York")]
+        [InlineData("Central Standard Time", "America/Chicago")]
+        [InlineData("Mountain Standard Time", "America/Denver")]
+        [InlineData("Pacific Standard Time", "America/Los_Angeles")]
+        [ConditionalTheory(nameof(SupportICUAndRemoteExecution))]
+        public static void TestTimeZoneNames(string windowsId, string ianaId)
+        {
+            RemoteExecutor.Invoke(static (wId, iId) =>
+            {
+                TimeZoneInfo info1, info2;
+                if (PlatformDetection.IsWindows)
+                {
+                    info1 = TimeZoneInfo.FindSystemTimeZoneById(iId);
+                    info2 = TimeZoneInfo.FindSystemTimeZoneById(wId);
+                }
+                else
+                {
+                    info1 = TimeZoneInfo.FindSystemTimeZoneById(wId);
+                    info2 = TimeZoneInfo.FindSystemTimeZoneById(iId);
+                }
+                Assert.Equal(info1.StandardName, info2.StandardName);
+                Assert.Equal(info1.DaylightName, info2.DaylightName);
+                Assert.Equal(info1.DisplayName, info2.DisplayName);
+            }, windowsId, ianaId).Dispose();
+        }
+
         private static bool IsEnglishUILanguage => CultureInfo.CurrentUICulture.Name.Length == 0 || CultureInfo.CurrentUICulture.TwoLetterISOLanguageName == "en";
 
         private static bool IsEnglishUILanguageAndRemoteExecutorSupported => IsEnglishUILanguage && RemoteExecutor.IsSupported;