patch 9.1.0497: termdebug can be further improved

Problem:  termdebug can be further improved
Solution: refactor save/restore, update docs,
          add a new save/restore test (Ubaldo Tiberi)

closes: #15032

Signed-off-by: Ubaldo Tiberi <ubaldo.tiberi@google.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/terminal.txt b/runtime/doc/terminal.txt
index e918394..83c8793 100644
--- a/runtime/doc/terminal.txt
+++ b/runtime/doc/terminal.txt
@@ -1,4 +1,4 @@
-*terminal.txt*	For Vim version 9.1.  Last change: 2024 Jun 17
+*terminal.txt*	For Vim version 9.1.  Last change: 2024 Jun 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -1524,6 +1524,9 @@
 	let g:termdebug_use_prompt = 1
 <
 Mappings ~
+The termdebug plugin enables a few default mappings.  All those mappings
+are reset to their original values once the termdebug session concludes.
+
 					*termdebug_map_K* *termdebug-mappings*
 The K key is normally mapped to |:Evaluate| unless a buffer local (|:map-local|)
 mapping to K already exists.  If you do not want this use: >