Treat System.Private.CoreLib as a system lib for extension method search

Author: T-Gro

src/Compiler/AbstractIL/ilread.fs

@@ -2148,6 +2148,7 @@ and typeDefReader ctxtH : ILTypeDefStored =
                     ctxt.fileName.EndsWith("System.Runtime.dll")
                     || ctxt.fileName.EndsWith("mscorlib.dll")
                     || ctxt.fileName.EndsWith("netstandard.dll")
+                    || ctxt.fileName.EndsWith("System.Private.CoreLib.dll")
 
                 while attrIdx <= attrsEndIdx && not containsExtensionMethods do
                     let mutable addr = ctxt.rowAddr TableNames.CustomAttribute attrIdx

tests/FSharp.Compiler.Private.Scripting.UnitTests/FSharpScriptTests.fs

@@ -352,6 +352,22 @@ tInput.Length
         let value = opt.Value
         Assert.Equal(4L, downcast value.ReflectionValue)
 
+    [<Fact>]
+    member _.``ML - use assembly with ref dependencies and without refing SMemory``() =
+        let code = """
+#r "nuget:Microsoft.ML.OnnxTransformer,1.4.0"
+
+open System
+open System.Numerics.Tensors
+let inputValues = [| 12.0; 10.0; 17.0; 5.0 |]
+let tInput = new DenseTensor<float>(inputValues.AsMemory(), new ReadOnlySpan<int>([|4|]))
+tInput.Length
+"""
+        use script = new FSharpScript(additionalArgs=[| "/usesdkrefs-" |])
+        let opt = script.Eval(code)  |> getValue
+        let value = opt.Value
+        Assert.Equal(4L, downcast value.ReflectionValue)
+
     [<Fact>]
     member _.``System.Device.Gpio - Ensure we reference the runtime version of the assembly``() =
         let code = """