Switch java_sdk_library to use SetDefaultableHook()

Previously, java_sdk_library used AddLoadHook() to register a hook that
when called would create its child modules. That meant the
java_sdk_library properties that were used to create the child modules,
e.g. sdk_version could not be defaulted because the modules are created
before the defaults are applied.

This change switches java_sdk_library to use the new
SetDefaultableHook() mechanism to register the hook instead of the
AddLoadHook() mechanism.

It also prevents the child modules from being created if the module has
been disabled.

Bug: 155295806
Test: m checkapi
Change-Id: Ic6f90eb4449338e549878f64e8119e286b9aa549