runtime(sh): refactored sh.vim syntax script

- unified bashStatement, kshStatement and shStatement as much as
  possible
- separated builtin commands from external programs
- cleaned up kornshell flavor logic
- fixed alias syntax highlighting
- added test for bash alias syntax highlighting
- removed daemon keyword

closes: #18355

Signed-off-by: Bjoern Foersterling <bjoern.foersterling@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/syntax/testdir/input/sh_sundrous.bash

@@ -54,4 +54,5 @@ uname
 uniq
 wc
 xargs
+# xgrep is neither a builtin for bash nor an external program
 xgrep