msvc: drop exception, make BIT() a bitfield with Visual Studio

Add casts to `bool`, or use `bit` type in local variables, where
neccessary to avoid MSVC compiler warnings C4242.

Note: There may remain places needing the above updates, where not
tested in CI, and missed in manual review.

Also:
- urldata: convert struct field `connect_only` to bitfield to match its
  counterpart in another struct.
- rename curl-specific `bit` type to `curl_bit`.

Closes #20142

lib/cf-socket.c

@@ -1263,7 +1263,7 @@ static CURLcode cf_tcp_connect(struct Curl_cfilter *cf,
     }
 
     /* Connect TCP socket */
-    rc = do_connect(cf, data, cf->conn->bits.tcp_fastopen);
+    rc = do_connect(cf, data, (bool)cf->conn->bits.tcp_fastopen);
     error = SOCKERRNO;
     set_local_ip(cf, data);
     CURL_TRC_CF(data, cf, "local address %s port %d...",