Create a product variable for skipping apex contribution contents

This denylist will be used to ignore the prebuilt google apexes listed
in apex_contributions of vendor/google/build when building aosp products
in next.

Test: in main, lunch aosp_cf_x86_64_phone-next-userdebug && m nothing
(with ag/25842580)
Bug: 308187268

Change-Id: I5330b44caf15193a00f1e255cef24b67c794382b
Merged-In: I5330b44caf15193a00f1e255cef24b67c794382b