ResourcePathShortener deterministically handles hash collisions

ResourcePathShortener appends one digit at the end of colliding short
file names to disambiguate them. This cl sorts the list of file paths so
that colliding files always get the same disambiguating digit from one
run to the next rather than possibly alternating.

Test: make aapt2_tests

Change-Id: I983a1448c21f2c79d7cdb1de232e7758c04fc256