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/job.c b/src/job.c
index 0ed33a7..e12f687 100644
--- a/src/job.c
+++ b/src/job.c
@@ -31,6 +31,8 @@
 	*modep = MODE_JS;
     else if (STRCMP(val, "json") == 0)
 	*modep = MODE_JSON;
+    else if (STRCMP(val, "lsp") == 0)
+	*modep = MODE_LSP;
     else
     {
 	semsg(_(e_invalid_argument_str), val);