Fix #803: Use relational patterns for VB Select Case

When converting a Visual Basic Select Case statement with a relational
clause (e.g., `Case Is < 1000`), the C# code converter used to output a
variable pattern with a when clause (e.g., `case var @case when @case < 1000:`).
With modern C#, this can be represented more concisely using relational
patterns (e.g., `case < 1000:`).

This commit modifies `MethodBodyExecutableStatementVisitor.cs` to map
Visual Basic relational case clauses to C# `RelationalPatternSyntax`,
`ConstantPatternSyntax` (for equality), and `UnaryPatternSyntax` (for
inequality using `not`).

It also updates existing tests that were affected by this change to
expect the new, cleaner syntax, and adds a test specific to Issue 803.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: GrahamTheCoder

Tests/CSharp/StatementTests/MethodStatementTests.cs

@@ -1,4 +1,4 @@
-using System.Threading.Tasks;
+using System.Threading.Tasks;
 using ICSharpCode.CodeConverter.Tests.TestRunners;
 using Xunit;
 
@@ -1089,13 +1089,13 @@ public static string TimeAgo(int daysAgo)
         {
             case var @case when 0 <= @case && @case <= 3:
             case 4:
-            case var case1 when case1 >= 5:
-            case var case2 when case2 < 6:
-            case var case3 when case3 <= 7:
+            case >= 5:
+            case < 6:
+            case <= 7:
                 {
                     return ""this week"";
                 }
-            case var case4 when case4 > 0:
+            case > 0:
                 {
                     return daysAgo / 7 + "" weeks ago"";
                 }
@@ -1249,15 +1249,15 @@ public void DoesNotThrow()
         var rand = new Random();
         switch (rand.Next(8))
         {
-            case var @case when @case < 4:
+            case < 4:
                 {
                     break;
                 }
             case 4:
                 {
                     break;
                 }
-            case var case1 when case1 > 4:
+            case > 4:
                 {
                     break;
                 }
@@ -1268,9 +1268,7 @@ public void DoesNotThrow()
                 }
         }
     }
-}
-1 target compilation errors:
-CS0825: The contextual keyword 'var' may only appear within a local variable declaration or in script code");
+}");
     }
 
     [Fact]
@@ -1786,6 +1784,64 @@ public void AllAssignmentOperators()
         set_Item(0, get_Item(0) >> 2);
         set_StrItem(0, get_StrItem(0) + "" World"");
     }
+}");
+    }
+
+    [Fact]
+    public async Task Issue803_SelectCaseWithRelationalPatternAsync()
+    {
+        await TestConversionVisualBasicToCSharpAsync(@"Class TestClass
+    Private Sub TestMethod(ByVal Breite As Integer)
+        Dim Rollo_FederUmdrehungen_Berechnen As Integer
+        Select Case Breite
+          Case Is < 1000
+            Rollo_FederUmdrehungen_Berechnen = 12
+          Case Is < 1200
+            Rollo_FederUmdrehungen_Berechnen = 15
+          Case Is < 1600
+            Rollo_FederUmdrehungen_Berechnen = 19
+          Case Is < 1800
+            Rollo_FederUmdrehungen_Berechnen = 25
+          Case Else
+            Rollo_FederUmdrehungen_Berechnen = 28
+        End Select
+    End Sub
+End Class", @"
+internal partial class TestClass
+{
+    private void TestMethod(int Breite)
+    {
+        int Rollo_FederUmdrehungen_Berechnen;
+        switch (Breite)
+        {
+            case < 1000:
+                {
+                    Rollo_FederUmdrehungen_Berechnen = 12;
+                    break;
+                }
+            case < 1200:
+                {
+                    Rollo_FederUmdrehungen_Berechnen = 15;
+                    break;
+                }
+            case < 1600:
+                {
+                    Rollo_FederUmdrehungen_Berechnen = 19;
+                    break;
+                }
+            case < 1800:
+                {
+                    Rollo_FederUmdrehungen_Berechnen = 25;
+                    break;
+                }
+
+            default:
+                {
+                    Rollo_FederUmdrehungen_Berechnen = 28;
+                    break;
+                }
+        }
+    }
 }");
     }
 }