Add HOST_PREFER_32_BIT to Soong Config and move art-tools to product configuration.

This change accomplishes two things:

Adds `HOST_PREFER_32_BIT` to Soong config variables:
The `HOST_PREFER_32_BIT` environment variable is frequently used in
Android.mk files within the art/ directory. By adding it to
soong_config_variable, we make it accessible to the Soong build system,
which will be essential when converting art modules to Android.bp.

Moves `art-tools` to product configuration:
Originally, `art-tools` was a phony target added to
PRODUCT_HOST_PACKAGES. This approach is incorrect because
PRODUCT_HOST_PACKAGES should only contain actual modules, not phony
targets. We are addressing this by converting the dependencies and
conditional statements (ifeq) within `art-tools` into
PRODUCT_HOST_PACKAGES entries in base_system.mk.

Bug: 346702835
Test: m -j; Then, check related dependencies build in the system.
Change-Id: Iab252dea71c9df9d75f2701b33d3cd4d391e7f5d