build: enable -Wformat-signedness, fix issues found

Adjust code to avoid `-Wformat-signedness` warnings, while making sure
that enums are always cast to a known type when passing them to `printf`
functions, to support compilers and compiler settings where enums are
not default-size signed ints.

- cast integers printed as hex to `unsigned`. (63 times, 20 of them in
  `mbedtls.c`)
- cast misc enums to `int` for printing. (31 times)
- cast `CURL_LOCK_DATA_*` enums to `int`. (4 times)
- cast `CURL_FORMADD_*` enums to `int`. (13 times)
- cast `CURLSHE_*` enums to `int`. (3 times)
- cast `CURLUE_*` enums to `int`. (33 times)
- cast `CURLMSG_*` enums to `int`. (6 times)
- cast `CURLE_*` enums to `int`. (~380 times)
- unit1675: fix mask.
  Follow-up to 7c34365cce #21879

Ref: #18343 (initial attempt)

Closes #20848

lib/content_encoding.c

@@ -820,7 +820,8 @@ CURLcode Curl_build_unencoding_stack(struct Curl_easy *data,
 
       result = Curl_cwriter_create(&writer, data, cwt, phase);
       CURL_TRC_WRITE(data, "added %s decoder %s -> %d",
-                     is_transfer ? "transfer" : "content", cwt->name, result);
+                     is_transfer ? "transfer" : "content", cwt->name,
+                     (int)result);
       if(result)
         return result;