patch 9.0.1962: No support for writing extended attributes

Problem:  No support for writing extended attributes
Solution: Add extended attribute support for linux

It's been a long standing issue, that if you write a file with extended
attributes and backupcopy is set to no, the file will loose the extended
attributes.

So this patch adds support for retrieving the extended attributes and
copying it to the new file. It currently only works on linux, mainly
because I don't know the different APIs for other systems (BSD, MacOSX and
Solaris).  On linux, this should be supported since Kernel 2.4 or
something, so this should be pretty safe to use now.

Enable the extended attribute support with normal builds.

I also added it explicitly to the :version output as well as make it
able to check using `:echo has("xattr")`, to have users easily check
that this is available.

In contrast to the similar support for SELINUX and SMACK support (which
also internally uses extended attributes), I have made this a FEAT_XATTR
define, instead of the similar HAVE_XATTR.

Add a test and change CI to include relevant packages so that CI can
test that extended attributes are correctly written.

closes: #306
closes: #13203

Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.0.  Last change: 2023 Aug 09
+*builtin.txt*	For Vim version 9.0.  Last change: 2023 Sep 27
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -11082,6 +11082,8 @@ winaltkeys		Compiled with 'winaltkeys' option.
 windows			Compiled with support for more than one window.
 			(always true)
 writebackup		Compiled with 'writebackup' default on.
+xattr			Compiled with extended attributes support |xattr|
+			(currently only supported on Linux).
 xfontset		Compiled with X fontset support |xfontset|.
 xim			Compiled with X input method support |xim|.
 xpm			Compiled with pixmap support.

runtime/doc/editing.txt

@@ -1,4 +1,4 @@
-*editing.txt*   For Vim version 9.0.  Last change: 2023 Sep 22
+*editing.txt*   For Vim version 9.0.  Last change: 2023 Sep 27
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -1097,6 +1097,13 @@ will get the ACL info of the original file.
    The ACL info is also used to check if a file is read-only (when opening the
 file).
 
+				*xattr* *E1506* *E1507* *E1508* *E1509*
+xattr stands for Extended Attributes  It is an advanced way to save metadata
+alongside the file in the filesystem.  It depends on the actual filesystem
+being used and Vim supports it only on a Linux system.
+   Vim attempts to preserve the extended attribute info when writing a file.
+The backup file will get the extended attribute of the original file.
+
 						*read-only-share*
 When MS-Windows shares a drive on the network it can be marked as read-only.
 This means that even if the file read-only attribute is absent, and the ACL

runtime/doc/tags

@@ -1483,6 +1483,7 @@ $quote	eval.txt	/*$quote*
 +wildmenu	various.txt	/*+wildmenu*
 +windows	various.txt	/*+windows*
 +writebackup	various.txt	/*+writebackup*
++xattr	various.txt	/*+xattr*
 +xfontset	various.txt	/*+xfontset*
 +xim	various.txt	/*+xim*
 +xpm	various.txt	/*+xpm*
@@ -4506,6 +4507,10 @@ E1502	builtin.txt	/*E1502*
 E1503	builtin.txt	/*E1503*
 E1504	builtin.txt	/*E1504*
 E1505	builtin.txt	/*E1505*
+E1506	editing.txt	/*E1506*
+E1507	editing.txt	/*E1507*
+E1508	editing.txt	/*E1508*
+E1509	editing.txt	/*E1509*
 E151	helphelp.txt	/*E151*
 E152	helphelp.txt	/*E152*
 E153	helphelp.txt	/*E153*
@@ -11224,6 +11229,7 @@ x-resources	version5.txt	/*x-resources*
 x11-clientserver	remote.txt	/*x11-clientserver*
 x11-cut-buffer	gui_x11.txt	/*x11-cut-buffer*
 x11-selection	gui_x11.txt	/*x11-selection*
+xattr	editing.txt	/*xattr*
 xf86conf.vim	syntax.txt	/*xf86conf.vim*
 xfontset	mbyte.txt	/*xfontset*
 xfree-xterm	syntax.txt	/*xfree-xterm*

runtime/doc/various.txt

@@ -1,4 +1,4 @@
-*various.txt*   For Vim version 9.0.  Last change: 2022 Dec 13
+*various.txt*   For Vim version 9.0.  Last change: 2023 Sep 27
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -503,6 +503,7 @@ T  *+windows*		more than one window; Always enabled since 8.0.1118.
 m  *+writebackup*	|'writebackup'| is default on
 m  *+xim*		X input method |xim|
    *+xfontset*		X fontset support |xfontset|
+N  *+xattr*		compiled with extended attribute support (Linux only)
    *+xpm*		pixmap support
 m  *+xpm_w32*		Win32 GUI only: pixmap support |w32-xpm-support|
    *+xsmp*		XSMP (X session management) support