Add file mapping to phpstan (#4685)

* PHPStan is now working with filename-mapping

See help ale-lint-other-machines for more info about filename-mapping.

* Add two tests to show and test what is expected

* Missed this update while creating previous commit

* Simplified the update

We only needed to refactor the processing loop.
No extra test are needed.

ale_linters/php/phpstan.vim

@@ -57,13 +57,15 @@ function! ale_linters#php#phpstan#Handle(buffer, lines) abort
         return l:output
     endif
 
-    for l:err in l:res.files[expand('#' . a:buffer .':p')].messages
+    for l:key in keys(l:res.files)
+        for l:err in l:res.files[l:key].messages
             call add(l:output, {
             \   'lnum': l:err.line,
             \   'text': l:err.message,
             \   'type': 'E',
             \})
         endfor
+    endfor
 
     return l:output
 endfunction