resourceloader: Move packaging to a new getModuleContent() method

resourceloader: Move packaging to a new getModuleContent() method

Centralise the building of module packages into this method so
that it can be easily re-used.

This is in preparation for providing the option for modules to use
content-based hashing (instead of based on meta-data) in the version
string of modules. Having a getModuleContent method allows that to
be implemented in a way that is well-cached (as we'll be calling it
from multiple multiple code paths) and without duplicating this logic.

Bug: T98087
Change-Id: I376233caaabe44b6101565b70a50904abdf8ab4f