patch 9.1.0934: hard to view an existing buffer in the preview window

Problem:  hard to view an existing buffer in the preview window
Solution: add the :pbuffer command (Yinzuo Jiang)

Similar as `:pedit` and `:buffer` command. `:pbuffer` edits buffer [N]
from the buffer list in the preview window.

`:pbuffer` can also open special buffer, for example terminal buffer.

closes: #16222

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/indent.txt b/runtime/doc/indent.txt
index 8f347d7..5f0893f 100644
--- a/runtime/doc/indent.txt
+++ b/runtime/doc/indent.txt
@@ -1,4 +1,4 @@
-*indent.txt*    For Vim version 9.1.  Last change: 2024 Nov 12
+*indent.txt*    For Vim version 9.1.  Last change: 2024 Dec 16
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar