patch 8.2.4648: handling LSP messages is a bit slow

Problem:    Handling LSP messages is a bit slow.
Solution:   Included support for LSP messages. (Yegappan Lakshmanan,
            closes #10025)
diff --git a/src/structs.h b/src/structs.h
index 192693b..36eb054 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -2193,6 +2193,7 @@
     MODE_RAW,
     MODE_JSON,
     MODE_JS,
+    MODE_LSP			// Language Server Protocol (http + json)
 } ch_mode_T;
 
 typedef enum {