Add per-direction wxSocket wait flags and byte counters.

Add per-direction wxSocket wait flags and byte counters.

Allow to specify whether the socket should block until all the data is read or
written or, on the contrary, avoid blocking only when reading or writing
instead of always using the same behaviour in both directions.

Also add separate counters for the bytes read/written instead of using the
same one for both.

These changes make it possible to use the same socket for reading/writing in
different threads.

Closes #14506.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72591 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775