pdl: add explicit versions to Cargo dependencies

Clap has released a version 4, but Android is currently on version 3.
The update in https://r.android.com/2241208 breaks if Clap 4 is used
by accident. By adding the current version numbers, we can guard
against these problems.

Test: cargo update && cargo test
Change-Id: I270adb4538a83748d477ee6091bc4a2605183f48