Jsonrpc: support some JSONesque non-JSONRPC protocols, like DAP

Jsonrpc: support some JSONesque non-JSONRPC protocols, like DAP

* lisp/jsonrpc.el (jsonrpc-convert-to-endpoint)
(jsonrpc-convert-from-endpoint): New generics.
(jsonrpc-connection-send): Call jsonrpc-convert-to-endpoint.
Rework logging.
(jsonrpc-connection-receive): Call jsonrpc-convert-from-endpoint.
Rework logging. jsonrpc--reply with METHOD.
(jsonrpc--log-event): Take subtype.
(Version): Bump to 1.0.19

* test/lisp/progmodes/eglot-tests.el (eglot--sniffing): Adapt
to new protocol of jsonrpc--log-event.

* doc/lispref/text.texi (JSONRPC Overview): Rework.