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

docs/examples/parseurl.c

@@ -51,7 +51,7 @@ int main(void)
   /* extract hostname from the parsed URL */
   uc = curl_url_get(h, CURLUPART_HOST, &host, 0);
   if(!uc) {
-    printf("Host name: %s\n", host);
+    printf("Hostname: %s\n", host);
     curl_free(host);
   }