runtime: make command name for &iskeywordprg more unique (#13297)

See https://github.com/vim/vim/pull/13213/commits by @dkearns:
Rename 'keywordprg' user command to ShKeywordPrg as this is just a
leaking implementation detail.

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/systemd.vim b/runtime/ftplugin/systemd.vim
index e60a5e4..8bcacdd 100644
--- a/runtime/ftplugin/systemd.vim
+++ b/runtime/ftplugin/systemd.vim
@@ -1,6 +1,7 @@
 " Vim filetype plugin file
 " Language:			systemd.unit(5)
 " Keyword Lookup Support:	Enno Nagel <enno.nagel+vim@gmail.com>
+" Latest Revision:      2023-10-07
 
 if !exists('b:did_ftplugin')
   " Looks a lot like dosini files.
@@ -9,11 +10,11 @@
 
 if has('unix') && executable('less')
   if !has('gui_running')
-    command -buffer -nargs=1 Sman silent exe '!' . KeywordLookup_systemd(<q-args>) | redraw!
+    command -buffer -nargs=1 SystemdKeywordPrg silent exe '!' . KeywordLookup_systemd(<q-args>) | redraw!
   elseif has('terminal')
-    command -buffer -nargs=1 Sman silent exe 'term ' . KeywordLookup_systemd(<q-args>)
+    command -buffer -nargs=1 SystemdKeywordPrg silent exe 'term ' . KeywordLookup_systemd(<q-args>)
   endif
-  if exists(':Sman') == 2
+  if exists(':SystemdKeywordPrg') == 2
     if !exists('*KeywordLookup_systemd')
       function KeywordLookup_systemd(keyword) abort
         let matches = matchlist(getline(search('\v^\s*\[\s*.+\s*\]\s*$', 'nbWz')), '\v^\s*\[\s*(\k+).*\]\s*$')
@@ -26,11 +27,11 @@
       endfunction
     endif
     setlocal iskeyword+=-
-    setlocal keywordprg=:Sman
+    setlocal keywordprg=:SystemdKeywordPrg
     if !exists('b:undo_ftplugin') || empty(b:undo_ftplugin)
       let b:undo_ftplugin = 'setlocal keywordprg< iskeyword<'
     else
-      let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer Sman'
+      let b:undo_ftplugin .= '| setlocal keywordprg< iskeyword< | sil! delc -buffer SystemdKeywordPrg'
     endif
   endif
 endif