Export some board config vars to autogenerate vendor-build.prop

As part of the automatic vendor.img soong module generation, we will
also autogenerate a vendor-build-$PRODUCT.prop and
andorid-info-$BOARD.prop soong module. These will eventually be
checked-in.

The kati vendor.img will still use the kati built vendor build.prop
file.

Bug: 374371755
Test: diff in contents for aosp_cf_x86_64_phone https://paste.googleplex.com/5766413037076480
Summary
- timestamp change (expected)
- ro.hwui.use_vulkan changes from "" to false, but I think this is
  functionally equivalent
Test: presubmits

Change-Id: I66dafadd286a5c6047dc99562ab32f72eda509ee