Jsonrpc: add new jsonrpc-autoport-bootstrap helper
This will help Eglot and some other extensions connect to network
servers that are started with a call to a local program.
* lisp/jsonrpc.el (jsonrpc--process-sentinel): Also delete inferior.
(jsonrpc-process-connection): Add -autoport-inferior slot.
(initialize-instance jsonrpc-process-connection): Check
process-creating function arity. Use jsonrpc-forwarding-buffer
(jsonrpc-autoport-bootstrap): New helper.
(Version): Bump to 1.0.20.