windows build: for the "setup" exe, put another "-debug" exe inside (#6603)
windows build: for the "setup" exe, put another "-debug" exe inside (#6603)

The "setup" Windows binary we distribute allows users to "install" Electrum
on their system. The distributable is created by NSIS. During
installation a bunch of files will get unpacked in %programfiles(x86)%/Electrum,
including an "inner" exe that will be the entrypoint for the user to start
the application. A shortcut is also created for the inner exe.

With this change, there will now be two inner EXEs. One the same as before,
the other with a "-debug" suffix in its name. The debug exe is built as a
"console" application (as opposed to a "windowed" application), so when
launched via double-click a black console window would appear; and also
importantly stdin/stdout are handled properly for it (unlike for "windowed"
programs). (see #2592)

There will not be a shortcut or similar for the debug exe; it would just
be there as a debugging option we can instruct users to use when needed.
In particular early crashes during startup are hard to debug without
stdout/stderr. (see e.g. #6601)
pooler/electrum-ltc,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,spesmilo/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona,spesmilo/electrum,spesmilo/electrum,pooler/electrum-ltc,pooler/electrum-ltc,wakiyamap/electrum-mona