"Speculative" keywords (discard, field) binding + private symbols in base type

[controlflow]

Version Used:

main branch 19.04.2022
features/semi-auto-props branch 19.04.2022

Steps to Reproduce:

Compile the following code:

class A {
  // all private
  private int _, field;
  private string nameof(int i) => "";
}

class B : A {
  int Property {
    get {
      var name = nameof(A); // OK
      _ = "discard"; // error, inaccessible
      return field; // error, inaccessible
    }
  }
}

https://sharplab.io/#v2:EYLgZgpghgLgrgJwgZwLTIgWwJaqnGAe1QAcFCTkAaAExAGoAfAAQCYACAQXYG8BYAFDt2AehHsoAG0nsy2AG6wIg4XMUwI7bADsY7APpV2YbBEk0A3CtkIFS9swCMABnbaomCITAAKHXuwASnYAXgA+dgAiSKsBAF9BQTZ2ACF2EC5ea392AAVyEggEGABPLKFhdgBzCD1+Csr2RQQ3D00Q1s9vH05Ai1FxAHkAaWtG/VCommxkAGMoBBoYgfYi8gQjHShZ2ZRkbGBJZQbK5gB2Y1NzfrFVhHXN9x29g6Ox9gSKz7igA===

Expected Behavior:

Compilation is OK, in class B the _ reference is a discard and field is a backing field reference.
I expect _ and field to work the same way nameof works - the compilation of B should not rely on seot of private APIs in type A.

Actual Behavior:

error CS0122: 'A._' is inaccessible due to its protection level
error CS0122: 'A.field' is inaccessible due to its protection level

[hez2010]

I think _ will become a lexical keyword in the language and cannot be used as identifiers in the future.
See: dotnet/csharplang#4460