badwords: check indented lines in source code, fix fallouts

- badwords.pl: add `-a` option to check all lines in source code files.
  Before this patch indented lines were skipped (to avoid Markdown code
  fences.)
- GHA/checksrc: use `-a` when verifying the source code.
- GHA/checksrc: disable `So` and `But` rules for source code.
- GHA/checksrc: add docs/examples to the verified sources.
- badwords.txt: delete 4 duplicates.
- badwords.txt: group and sort contractions.
- badwords.txt: allow ` url = `, `DIR`, `<file name`.

Closes #19536

lib/cookie.c

@@ -458,7 +458,7 @@ parse_cookie_header(struct Curl_easy *data,
        */
 
       if(!co->name) {
-        /* The very first name/value pair is the actual cookie name */
+        /* The first name/value pair is the actual cookie name */
         if(!sep)
           /* Bad name/value pair. */
           return CURLE_OK;