patch 9.0.0756: no autocmd event for changing text in a terminal window

Problem:    No autocmd event for changing text in a terminal window.
Solution:   Add TextChangedT. (Shougo Matsushita, closes #11366)
diff --git a/src/autocmd.c b/src/autocmd.c
index 93da0bb..cf0f094 100644
--- a/src/autocmd.c
+++ b/src/autocmd.c
@@ -182,6 +182,7 @@
     {"TextChanged",	EVENT_TEXTCHANGED},
     {"TextChangedI",	EVENT_TEXTCHANGEDI},
     {"TextChangedP",	EVENT_TEXTCHANGEDP},
+    {"TextChangedT",	EVENT_TEXTCHANGEDT},
     {"User",		EVENT_USER},
     {"VimEnter",	EVENT_VIMENTER},
     {"VimLeave",	EVENT_VIMLEAVE},