Add a function for getting matches, and use it to simplify a lot of code

ale_linters/dockerfile/hadolint.vim

@@ -7,13 +7,7 @@ function! ale_linters#dockerfile#hadolint#Handle(buffer, lines) abort
     let l:pattern = '\v^/dev/stdin:?(\d+)? (\S+) (.+)$'
     let l:output = []
 
-    for l:line in a:lines
-        let l:match = matchlist(l:line, l:pattern)
-
-        if len(l:match) == 0
-            continue
-        endif
-
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
         let l:lnum = 0
 
         if l:match[1] !=# ''