[expo-cli] Generate-module fixes and improvements

[barthap]

Why

Continuation of #2510 (that fix was rather critical). Trying to make expo generate-module more universal and generic.

Changes

• Android test files are now properly renamed
• Java package is now automatically detected based on directory structure
• NPM template package name accepts templates with tags @next and @latest (shall we make it less restrictive to accept any string as tag?)
• Package names are now properly handled regardless of having expo- prefix.
• iOS pod name always defaults to EXPackageName (it didn't always add EX prefix before) - idk if it's desirable change.
• IO optimizations - parallelised some file processing.

Test plan

Tested manually using custom testing template (custom package names etc). Checked if all renamings work as expected.