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/altsvc.c

@@ -559,7 +559,7 @@ CURLcode Curl_altsvc_parse(struct Curl_easy *data,
             }
           }
           else {
-            /* IPv6 host name */
+            /* IPv6 hostname */
             if(curlx_str_until(&p, &dsthost, MAX_IPADR_LEN, ']') ||
                curlx_str_single(&p, ']')) {
               infof(data, "Bad alt-svc IPv6 hostname, ignoring.");