Refactor *-select-bitness-of-required-modules

* Streamline required module bitness resolution

If a module is for cross host OS, the required modules are also for that
OS.
Otherwise if the requirer module is native and the required module is
shared library or native test, then the required module resolves to the
same bitness.
Otherwise the required module resolves to both variants, if they exist.

* Factor out the common logic and merge
  <target|host|host-cross>-select-bitness-of-required-modules

This lays the road for follow-up changes to add bitness suffix support.
This slightly reduces readibility. To make up for the loss, the
bitness-resolving logic is easier to maintain since we don't have
multiple copies of *-select-bitness-of-required-modules.

Bug: 155869107
Test: check the diff of product_target_FILES and product_host_FILES
Test: check the diff of ALL_MODULES.*.REQUIRED_FROM_(TARGET|HOST)
Change-Id: Ib2f4b548535e983d621dad71cb920101111140f2