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/cw-out.c

@@ -458,7 +458,7 @@ bool Curl_cw_out_is_paused(struct Curl_easy *data)
     return FALSE;
 
   ctx = (struct cw_out_ctx *)cw_out;
-  return ctx->paused;
+  return (bool)ctx->paused;
 }
 
 static CURLcode cw_out_flush(struct Curl_easy *data,