patch 8.2.2508: cannot change the character displayed in non existing lines

Problem:    Cannot change the character displayed in non existing lines.
Solution:   Add the "eob" item to 'fillchars'. (closes #7832, closes #3820)
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index ee5ee26..08d205c 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -3235,7 +3235,7 @@
 	Only normal file name characters can be used, "/\*?[|<>" are illegal.
 
 						*'fillchars'* *'fcs'*
-'fillchars' 'fcs'	string	(default "vert:|,fold:-")
+'fillchars' 'fcs'	string	(default "vert:|,fold:-,eob:~")
 			global
 			{not available when compiled without the |+folding|
 			feature}
@@ -3248,6 +3248,7 @@
 	  vert:c	'|'		vertical separators |:vsplit|
 	  fold:c	'-'		filling 'foldtext'
 	  diff:c	'-'		deleted lines of the 'diff' option
+	  eob:c		'~'		empty lines below the end of a buffer
 
 	Any one that is omitted will fall back to the default.  For "stl" and
 	"stlnc" the space will be used when there is highlighting, '^' or '='
@@ -3267,6 +3268,7 @@
 	  vert:c	VertSplit		|hl-VertSplit|
 	  fold:c	Folded			|hl-Folded|
 	  diff:c	DiffDelete		|hl-DiffDelete|
+	  eob:c		EndOfBuffer		|hl-EndOfBuffer|
 
 		*'fixendofline'* *'fixeol'* *'nofixendofline'* *'nofixeol'*
 'fixendofline' 'fixeol'	boolean	(default on)
diff --git a/runtime/doc/todo.txt b/runtime/doc/todo.txt
index a731211..dd2ed70 100644
--- a/runtime/doc/todo.txt
+++ b/runtime/doc/todo.txt
@@ -776,8 +776,6 @@
 highlight name.  Esp. for the statusline.
 And "extends" and "precedes" are also useful without 'list' set.  Also in
 'fillchars' or another option?
-Related: #3820 - Support setting the character displayed below the last line?
-Neovim uses "eob:X" in 'fillchars'.
 
 Sourceforge Vim pages still have content, redirect from empty page.
 Check for PHP errors. (Wayne Davison, 2018 Oct 26)
diff --git a/runtime/doc/windows.txt b/runtime/doc/windows.txt
index 2a31526..69de9ba 100644
--- a/runtime/doc/windows.txt
+++ b/runtime/doc/windows.txt
@@ -138,10 +138,12 @@
 that have termcap codes for italics.
 
 							*filler-lines*
-The lines after the last buffer line in a window are called filler lines.
-These lines start with a tilde (~) character. By default, these are
-highlighted as NonText (|hl-NonText|). The EndOfBuffer highlight group
-(|hl-EndOfBuffer|) can be used to change the highlighting of filler lines.
+The lines after the last buffer line in a window are called filler lines.  By
+default, these lines start with a tilde (~) character. The 'eob' item in the
+'fillchars' option can be used to change this character. By default, these
+characters are highlighted as NonText (|hl-NonText|). The EndOfBuffer
+highlight group (|hl-EndOfBuffer|) can be used to change the highlighting of
+the filler characters.
 
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 3. Opening and closing a window				*opening-window* *E36*