Remove connection grabbing antics from jsonrpc.el

Remove connection grabbing antics from jsonrpc.el

* eglot.el (eglot--managed-mode): Don't touch
jsonrpc-find-connection-functions.
(eglot--current-server-or-lose, eglot--current-server): New
functions (resuscitate).
(eglot-shutdown, eglot, eglot-reconnect)
(eglot--server-capable, eglot--maybe-activate-editing-mode)
(eglot-clear-status, eglot--mode-line-format)
(eglot--signal-textDocument/didChange)
(eglot--signal-textDocument/didOpen)
(eglot--signal-textDocument/didSave)
(xref-backend-identifier-completion-table)
(xref-backend-definitions, xref-backend-references)
(xref-backend-apropos, eglot-completion-at-point)
(eglot-help-at-point, eglot-eldoc-function, eglot-imenu)
(eglot-rename, eglot-code-actions): Use eglot--current-server and
eglot--current-server-or-lose.
(eglot-events-buffer, eglot-stderr-buffer)
(eglot-forget-pending-continuations): New commands.
(eglot--mode-line-format): Use eglot-stderr-buffer.

* jsonrpc.el (jsonrpc-find-connection-functions)
(jsonrpc-current-connection, jsonrpc-current-connection-or-lose):
Remove.
(jsonrpc-stderr-buffer, jsonrpc-events-buffer): Simplify.
(jsonrpc-forget-pending-continuations): No longer interactive.

* eglot-tests.el (auto-detect-running-server, auto-reconnect): Use
eglot--current-server.