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
diff --git a/runtime/doc/index.txt b/runtime/doc/index.txt
index c595d9d..e1f68a0 100644
--- a/runtime/doc/index.txt
+++ b/runtime/doc/index.txt
@@ -1,4 +1,4 @@
-*index.txt*     For Vim version 9.1.  Last change: 2023 Jul 14
+*index.txt*     For Vim version 9.1.  Last change: 2024 Dec 15
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1529,6 +1529,7 @@
 |:ownsyntax|	:ow[nsyntax]	set new local syntax highlight for this window
 |:packadd|	:pa[ckadd]	add a plugin from 'packpath'
 |:packloadall|	:packl[oadall]	load all packages under 'packpath'
+|:pbuffer|	:pb[uffer]	edit buffer in the preview window
 |:pclose|	:pc[lose]	close preview window
 |:pedit|	:ped[it]	edit file in the preview window
 |:perl|		:pe[rl]		execute Perl command
diff --git a/runtime/doc/tags b/runtime/doc/tags
index 9f46c6e..a8b4987 100644
--- a/runtime/doc/tags
+++ b/runtime/doc/tags
@@ -3026,6 +3026,8 @@
 :packadd	repeat.txt	/*:packadd*
 :packl	repeat.txt	/*:packl*
 :packloadall	repeat.txt	/*:packloadall*
+:pb	windows.txt	/*:pb*
+:pbuffer	windows.txt	/*:pbuffer*
 :pc	windows.txt	/*:pc*
 :pclose	windows.txt	/*:pclose*
 :pe	if_perl.txt	/*:pe*
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index 7691142..bcda3d0 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2024 Dec 06
+*version9.txt*  For Vim version 9.1.  Last change: 2024 Dec 16
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41661,7 +41661,8 @@
 Commands: ~
 
 |[r| and |]r|		to move the cursor to previous/next rare word
-
+|:pbuffer|		Edit buffer [N] from the buffer list in the preview
+			window
 
 Options: ~
 
diff --git a/runtime/doc/windows.txt b/runtime/doc/windows.txt
index edb105a..7764072 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -1,4 +1,4 @@
-*windows.txt*   For Vim version 9.1.  Last change: 2024 Dec 14
+*windows.txt*   For Vim version 9.1.  Last change: 2024 Dec 16
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1005,6 +1005,15 @@
 		it.  Make the new Preview window (if required) N high.  If N is
 		not given, 'previewheight' is used.
 
+							*:pb* *:pbuffer*
+:[N]pb[uffer][!] [+cmd] [N]
+		Edit buffer [N] from the buffer list in the preview window.
+		If [N] is not given, the current buffer remains being edited.
+		See |:buffer-!| for [!].  This will also edit a buffer that is
+		not in the buffer list, without setting the 'buflisted' flag.
+		The notation with single quotes does not work here, `:pbuffer
+		12'345'` uses 12'345 as a buffer name.  Also see |+cmd|.
+
 							*:ped* *:pedit*
 :ped[it][!] [++opt] [+cmd] {file}
 		Edit {file} in the preview window.  The preview window is