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/connect-to.c

@@ -40,7 +40,7 @@ int main(void)
   /*
     Each single string should be written using the format
     HOST:PORT:CONNECT-TO-HOST:CONNECT-TO-PORT where HOST is the host of the
-    request, PORT is the port of the request, CONNECT-TO-HOST is the host name
+    request, PORT is the port of the request, CONNECT-TO-HOST is the hostname
     to connect to, and CONNECT-TO-PORT is the port to connect to.
    */
   /* instead of curl.se:443, it resolves and uses example.com:443 but in other
@@ -53,12 +53,12 @@ int main(void)
     curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
     curl_easy_setopt(curl, CURLOPT_URL, "https://curl.se/");
 
-    /* since this connects to the wrong host, checking the host name in the
+    /* since this connects to the wrong host, checking the hostname in the
        server certificate fails, so unless we disable the check libcurl
        returns CURLE_PEER_FAILED_VERIFICATION */
     curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
 
-    /* Letting the wrong host name in the certificate be okay, the transfer
+    /* Letting the wrong hostname in the certificate be okay, the transfer
        goes through but (most likely) causes a 404 or similar because it sends
        an unknown name in the Host: header field */
     res = curl_easy_perform(curl);