Feat: replace em dash with -- (#5125)

* no em dash
* add tests

autoload/ale/fix/registry.vim

@@ -207,6 +207,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['puppet'],
 \       'description': 'Run puppet-lint -f on a file.',
 \   },
+\   'replace_emdash': {
+\       'function': 'ale#fixers#generic#ReplaceEmDash',
+\       'suggested_filetypes': [],
+\       'description': 'Replace em dash with -- ASCII characters.',
+\   },
 \   'remove_trailing_lines': {
 \       'function': 'ale#fixers#generic#RemoveTrailingBlankLines',
 \       'suggested_filetypes': [],

autoload/ale/fixers/generic.vim

@@ -1,6 +1,10 @@
 " Author: w0rp <devw0rp@gmail.com>
 " Description: Generic functions for fixing files with.
 
+function! ale#fixers#generic#ReplaceEmDash(buffer, lines) abort
+    return map(copy(a:lines), {_, line -> substitute(line, "\u2014", '--', 'g')})
+endfunction
+
 function! ale#fixers#generic#RemoveTrailingBlankLines(buffer, lines) abort
     let l:end_index = len(a:lines) - 1