feat: implicitly focus entry on no focus request sent

[Myriad-Dreamin]

After opening the file it doesn't show the error unless I save the file (no-op).

vscode invokes lsp's focus command but neovim doesn't. should add an issue, and discuss a suitable behavior to change focus file if the client is neovim.

It is nice if client focus entry explicitly, however neovim/helix/zed clients don't do that. Adding many activity hooks to track activating document status if a client is not performing any focus command request.

We do want to focus the file implicitly by textDocument/diagnostic (pullDiagnostics mode), as suggested by language-server-protocol#718, however, this has poor support, e.g. since neovim 0.10.0.

See microsoft/language-server-protocol#718