Make c-u m-. work half decently

Make c-u m-. work half decently

* NEWS.md: Mention change.

* eglot.el (eglot--lsp-interface-alist): Add WorkspaceSymbol
(eglot--workspace-symbols-cache): New variable.
(eglot--recover-workspace-meta): New helper.
(xref-backend-identifier-completion-table): Complicate.
(xref-backend-definitions): Complicate.
(completion-category-overrides): Register a category and a style here.
(completion-styles-alist): Add eglot--lsp-backend-style style
(eglot--lsp-backend-style-call): New funtion.
(eglot--lsp-backend-style-all-completions): New function.
(eglot--lsp-backend-style-try-completion): New function.

GitHub-reference: fix https://github.com/joaotavora/eglot/issues/131