Add "updatable" property to ApexModule interface.

For a given variant of a module that implements ApexModule interface,
the "updatable" property tests if this variant comes from an updatable
apex. For platform variants it is always false.

Test: lunch aosp_walleye-userdebug && m nothing
Bug: 138994281
Merged-In: I2d4c54fb397e29dc9b3203be7fb17be4536529f7
Change-Id: I2d4c54fb397e29dc9b3203be7fb17be4536529f7
Exempt-From-Owner-Approval: cp from aosp
(cherry picked from commit 7c140d82)