Unbreak Eglot, Jsonrpc as EIEIO inches closer to CLOS (bug#67480)

EIEIO is an innacurate emulation of CLOS in many aspects and one of
them in accessor definition.  Before this commit

commit 6c47931a1a
Author: Brandon <brandon.irizarry@gmail.com>
Date:   Sat Nov 4 17:11:32 2023 -0400

    Make EIEIO ':accessor' behave like ':reader' when reading (bug#66938)

An :initform-less, non-:initarg'ed slot with be read using an
:accessor which would just return nil.  This is EIEIO specific of
course, but it made for (my) sloppy programming in jsonrpc.el and
eglot.el.

Tightening up the rules a bit meant these things broke and now I'm
fixing them.

* lisp/jsonrpc.el (jsonrpc-connection): Add a bunch of :initform nil
(jsonrpc-process-connection): Add a bunch of :initform nil

* lisp/progmodes/eglot.el (eglot-lsp-server): Add a bunch of :initform nil

lisp/jsonrpc.el

@@ -64,6 +64,7 @@
     :initarg :notification-dispatcher
     :documentation "Dispatcher for remotely invoked notifications.")
    (last-error
+    :initform nil
     :accessor jsonrpc-last-error
     :documentation "Last JSONRPC error message received from endpoint.")
    (-request-continuations
@@ -71,6 +72,7 @@
     :accessor jsonrpc--request-continuations
     :documentation "A hash table of request ID to continuation lambdas.")
    (-events-buffer
+    :initform nil
     :accessor jsonrpc--events-buffer
     :documentation "A buffer pretty-printing the JSONRPC events")
    (-events-buffer-scrollback-size
@@ -353,6 +355,7 @@ ignored."
     :initarg :process :accessor jsonrpc--process
     :documentation "Process object wrapped by the this connection.")
    (-expected-bytes
+    :initform nil
     :accessor jsonrpc--expected-bytes
     :documentation "How many bytes declared by server.")
    (-on-shutdown