Since the Mozart package requires PHP 7.2, and we need to support 7.0
and 7.1, the moving step has been removed from the composer install
stage. Instead, now it has to be triggered manually via
`composer run move-vendor-namespaces`, and the moved package must be
added to source control. See the updated src/Internal/Vendor/REAMDE.md
for details.
A custom fork of the coenjacobs/mozart package is now used to change
the namespace of the appropriate packages (only league/container
for now) instead of the previously used prefix-vendor-namespaces script.
The packages are now moved to the src/Internal/Vendor namespace instead
of being modified in-place in the vendor directory. The namespaces
are thus now prefixed with Automattic\WooCommerce\Internal\Vendor
(previously it was just Automattic\WooCommerce\Vendor).