Move dep on PRODUCT_COPY_FILES to main.mk

Prior to this change the product-installed-files macro didn't include
PRODUCT_COPY_FILES, which is a problem for the artifact path
enforcements. Fix this by moving the dep on PCF into main.mk.

Leave the declaration in Makefile for now.

Test: diff modules_to_install before and after
Bug: 80410283
Change-Id: Ie7ecd5a963aedd2c573f4fe46d327829908aec03