Report serverInfo (name and version) in the initialize result

Nobody has claimed this yet.

**Is your feature request related to a problem? Please describe.**

A client, or a proxy in front of the server, cannot tell from the LSP handshake which server it is talking to or which version: pyright's `InitializeResult` has no `serverInfo`. The name and version appear only in the startup `window/logMessage` ("Pyright language server 1.1.412 starting"), which a client has to parse. `serverInfo` has been a standard field since LSP 3.15, and basedpyright already returns it.

**Describe the solution you'd like**

`InitializeResult.serverInfo = { name: productName, version }` in `LanguageServerBase.initialize` (`packages/pyright-internal/src/languageServerBase.ts`). It is a four-line change; I have it ready and can open a PR if this is acceptable.

**Additional context**

I use it in lsp-det (https://github.com/tagawa0525/lsp-det), a proxy that selects a per-server readiness mapping by the server's name and version. Today it has to read pyright's startup log for that.

Start in packages/pyright-internal/src/languageServerBase.ts at LanguageServerBase.initialize and inspect how the LSP InitializeResult is assembled. Verify the server name comes from productName and the version from the existing server version value, then confirm the initialize response exposes both fields without changing the startup log behavior.

Written by the indexing model from the issue text.