Handle case when :textdocumentsync isn't a number

Also closes joaotavora/eglot#87.

* eglot.el (eglot--signal-textDocument/didChange): Grab :change
from :textDocumentSync server capability.

GitHub-reference: close joaotavora/eglot#86

lisp/progmodes/eglot.el

@@ -1191,7 +1191,9 @@ When called interactively, use the currently active server"
   "Send textDocument/didChange to server."
   (when eglot--recent-changes
     (let* ((server (eglot--current-server-or-lose))
-           (sync-kind (eglot--server-capable :textDocumentSync))
+           (sync-capability (eglot--server-capable :textDocumentSync))
+           (sync-kind (if (numberp sync-capability) sync-capability
+                        (plist-get sync-capability :change)))
            (full-sync-p (or (eq sync-kind 1)
                             (eq :emacs-messup eglot--recent-changes))))
       (jsonrpc-notify