coin: Print the failed vcpkg build logs on port installation failure

When a vcpkg port fails to build during provisioning, vcpkg only
prints the paths of the logs of the failed step, e.g.

See logs for more information:
 ./vcpkg-2026.06.01-qt/buildtrees/abseil/install-x64-osx-dbg-out.log

vcpkg has no option to print them, it's been an open feature request
since 2019 (I opened it!).

vcpkg's portfile helpers record the paths of those logs in
buildtrees/<port>/error-logs-<triplet>.txt.

Add a helper script for unix and for windows that reads these files
and prints the contents of the listed logs.
Call this code from the vcpkg port installation scripts when
'vcpkg install' fails.

Make sure to skip the CMakeCache.txt and CMakeConfigureLog.yaml logs
that are listed on configure failures. They are large and the actual
error is in the -out and -err logs. We can bring them back later if
need be.

Pick-to: 6.8 6.12
Change-Id: I5552e69b85cf85572078a79ee9252de8c4e800fe
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>