[TIMOB-26144] Android: Improve File.getDirectoryListing() performance in Resources directory

*Summary:* On Android, accessing files/directories under "Resources" is slower than it should be. These files are stored within the APK where a list of file paths from "assets" can be easily extracted... which should make it faster than storage access. *Test:* Run the below code to fetch a listing of all files under the "Resources" directory. Observe the log for the duration of this function.

var startTime = new Date();
var file = Ti.Filesystem.getFile(Ti.Filesystem.getResourcesDirectory());
var listing = file.getDirectoryListing();
Ti.API.info("@@@ getDirectoryListing() duration: " + (new Date() - startTime));

*Results:* For a project have about 160 files under "Resources", I get the following results... * Android 4.1 Emulator: 80 ms * Galaxy Nexus (Android 4.1): 70 ms * Amazon Fire HD 8 (7th Generation): 19 ms * Pixel XL (Android 8.0): 3 ms *Recommended Solution:* An Android APK is really a zip file. We should open the APK as a zip file and fetch/store all zip entries referencing files under the "assets" directory. This way we can have fast hash table lookups when doing existence checks and fetching directory listings.