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/runtime/doc/autocmd.txt b/runtime/doc/autocmd.txt
index 61db274..5051cc3 100644
--- a/runtime/doc/autocmd.txt
+++ b/runtime/doc/autocmd.txt
@@ -409,6 +409,7 @@
 			when popup menu is not visible
 |TextChangedP|		after a change was made to the text in Insert mode
 			when popup menu visible
+|TextChangedT|		after a change was made to the text in Terminal mode
 |TextYankPost|		after text has been yanked or deleted
 
 |SafeState|		nothing pending, going to wait for the user to type a
@@ -1237,6 +1238,10 @@
 				current buffer in Insert mode, only when the
 				popup menu is visible.  Otherwise the same as
 				TextChanged.
+							*TextChangedT*
+TextChangedT			After a change was made to the text in the
+				current buffer in Terminal mode.
+				Otherwise the same as TextChanged.
 							*TextYankPost*
 TextYankPost			After text has been yanked or deleted in the
 				current buffer.  The following values of