C#: Use modifier to decide, if a type is a record like type and implement support for record struct types.

csharp/ql/lib/semmle/code/cil/Types.qll

@@ -61,7 +61,7 @@ class Class extends ValueOrRefType {
 }
 
 /** A `record`. */
-class Record extends Class {
+deprecated class Record extends Class {
   Record() { this.isRecord() }
 }
 

csharp/ql/lib/semmle/code/csharp/Type.qll

@@ -372,6 +372,8 @@ class ValueOrRefType extends DotNet::ValueOrRefType, Type, Attributable, @value_
     nested_types(this, _, result)
   }
 
+  override predicate isRecord() { this.hasModifier("record") }
+
   override string toString() { result = Type.super.toString() }
 }
 
@@ -711,6 +713,20 @@ class Struct extends ValueType, @struct_type {
   override string getAPrimaryQlClass() { result = "Struct" }
 }
 
+/**
+ * A `record struct`, for example
+ * ```csharp
+ * record struct RS {
+ *   ...
+ * }
+ * ```
+ */
+class RecordStruct extends Struct {
+  RecordStruct() { this.isRecord() }
+
+  override string getAPrimaryQlClass() { result = "RecordStruct" }
+}
+
 /**
  * A reference type.
  *