C#: Add test for interpolated strings, where newlines are used in the provided expression.

Author: michaelnebel

csharp/ql/test/library-tests/csharp11/Strings.cs

@@ -0,0 +1,13 @@
+using System;
+
+public class MyTestClass
+{
+    public string M1(int x)
+    {
+        return $"This is my int {x switch
+        {
+            42 => "forty two",
+            _ => "something else"
+        }}.";
+    }
+}

csharp/ql/test/library-tests/csharp11/strings.expected

@@ -0,0 +1,3 @@
+| Strings.cs:7:16:11:12 | $"..." | Strings.cs:7:18:7:32 | "This is my int " |
+| Strings.cs:7:16:11:12 | $"..." | Strings.cs:7:34:11:9 | ... switch { ... } |
+| Strings.cs:7:16:11:12 | $"..." | Strings.cs:11:11:11:11 | "." |

csharp/ql/test/library-tests/csharp11/strings.ql

@@ -0,0 +1,6 @@
+import csharp
+
+query predicate interpolatedstrings(InterpolatedStringExpr se, Expr e) {
+  se.getFile().getStem() = "Strings" and
+  (e = se.getAText() or e = se.getAnInsert())
+}