Open static named literals can't be used in pattern matching

Named literals brought into scope by `open`ing a static class can't be used for pattern matching.

**Repro steps**

1. Open a static class that contains named literals as members. (F# can't currently define named literals as public class members, but `System.Math` will do for the repro.)
2. Try to use a named literal from that class in a match expression.

Repro code:

```F#
open type System.Math

let isPi x = match x with PI -> true | _ -> false
```

**Expected behavior**

The named literal is actually matched as a literal expression.

**Actual behavior**

The name of the literal introduces a new variable binding.

**Known workarounds**

Either qualify the named literal (`System.Math.PI`) or redefine the literal in the current module (`let [] PI = PI`).

**Related information**

* .NET Core SDK 3.1.100 (also in 3.0.100)
* `preview` of course.