moving apidiff out of preview (#3595)

release-notes/3.0/api-diff/.Net/3.0.0_System.Diagnostics.CodeAnalysis.md

@@ -0,0 +1,38 @@
+# System.Diagnostics.CodeAnalysis
+
+``` diff
+ namespace System.Diagnostics.CodeAnalysis {
++    public sealed class AllowNullAttribute : Attribute {
++        public AllowNullAttribute();
++    }
++    public sealed class DisallowNullAttribute : Attribute {
++        public DisallowNullAttribute();
++    }
++    public sealed class DoesNotReturnAttribute : Attribute {
++        public DoesNotReturnAttribute();
++    }
++    public sealed class DoesNotReturnIfAttribute : Attribute {
++        public DoesNotReturnIfAttribute(bool parameterValue);
++        public bool ParameterValue { get; }
++    }
++    public sealed class MaybeNullAttribute : Attribute {
++        public MaybeNullAttribute();
++    }
++    public sealed class MaybeNullWhenAttribute : Attribute {
++        public MaybeNullWhenAttribute(bool returnValue);
++        public bool ReturnValue { get; }
++    }
++    public sealed class NotNullAttribute : Attribute {
++        public NotNullAttribute();
++    }
++    public sealed class NotNullIfNotNullAttribute : Attribute {
++        public NotNullIfNotNullAttribute(string parameterName);
++        public string ParameterName { get; }
++    }
++    public sealed class NotNullWhenAttribute : Attribute {
++        public NotNullWhenAttribute(bool returnValue);
++        public bool ReturnValue { get; }
++    }
+ }
+```
+