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_09.sh

@@ -16,4 +16,5 @@
 ( cd ${HOME} ; $pwd ) | wc -c
 ( cd ${HOME} ) | wc -c
 ((n=1+2))
+# this is a syntax error, "let" is not a keyword in dash
 let n=1+2