Add "type" to textDocument/references results

VS Code issue (UI) is at https://github.com/microsoft/vscode/issues/74237

The C/C++ extension wants to be able to send back references of different types that users can determine what "type" of reference it is and filter out unwanted types -- in order to provide functionality equivalent to Visual Studio 2019. The types we want are below. Feel free to change the naming of the example types.

1. Confirmed reference (i.e. passes semantic checking): e.g. Type.ConfirmedReference
2. Not a reference (i.e. has the same name, but fails semantic checking -- these non-references might be desired in some cases), e.g. e.g. Type.NotAReference
3. Reference in a comment, e.g. e.g. Type.CommentReference
4. Reference in a string, e.g. Type.StringReference
5. Reference in an inactive (preprocessor) region, e.g. Type.InactiveReference (Note: Comment/String references take precedence, so this only applies to identifiers).
6. Confirmation in progress, e.g. Type.PendingReference
7. Cannot confirm reference (due to some bug or "by design" limitation), e.g. Type.UnknownReference

It's possible other reference types might be desirable as well for other languages or scenarios.

This is the screenshot from VS:

Our current "workaround" is to either send back multiple "types" merged together (ambiguously) or allow users to filter out types via a setting or a progress UI button, e.g. "show confirmed references", "show unconfirmed references" (i.e. 6 and 7).

The relevant LSP that would need to be changed is at
https://microsoft.github.io/language-server-protocol/specification#textDocument_references

Start by reading the textDocument/references section of the Language Server Protocol specification linked in the issue and compare the current result shape with the requested reference categories. Done means agreeing on an extensible type representation and documenting the updated protocol behavior, including how clients can distinguish the proposed reference kinds.