Simplify the officialbuild.bat script by only checking for "vcXX" instead of
accepting both them and "vsYYYY".
Also add instructions for using it in the corresponding HOWTO.
Closes#17514.
Use a single script for all compiler versions, another simple script just
defining wxWidgets version and, finally, a script building all the binaries
for all the compilers.
Closes#17510.
