The package_from_installed.py script didn't run under Python 3. This
change fixes that and this script now _requires_ Python 3. Requiring
Python 3 was simpler than supporting both, and there is no need to
maintain Python 2.7 support. This script is only ever invoked manually
and all machines it is run on should have Python 3.

Changes included using universal_newlines=True so that
subprocess.check_output returns a string instead of bytes, and
by explicitly converting dict.items() to a list.

Similarly, open(name, 'wb') was changed to open(name,'wt', newline='')
to avoid byte/str problems while still avoiding CR/LF translations.

This also changes the default Windows 10 SDK version to something more
recent - the current version that we build with.

To test:

  python3 package_from_installed.py -d 2019

The use of '-d' makes the script run in test mode which is much faster.

Change-Id: I2e3fc4d464f2914ba5ae36f0a78570ea7e5d4f03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2224506Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>