Use eng build's build time in `aapt2 version`

The binary build time is encoded in `android::build::GetBuildNumber()`
and we parse it from there to include "eng.yyyyMM" in the fingerprint
for eng builds.

Bug: 200741997
Test: Ran `aapt2 version` and output was:
Android Asset Packaging Tool (aapt) 2.19-eng.202307

Change-Id: I02e6d28ae8f59b4689b108387355f11045c92c65