pdl: Add canonical tests for variable sized arrays

This covers arrays with scalars, enums, and structs.

Tag: #feature
Bug: 233340325
Test: atest pdl_tests pdl_rust_generator_tests_{le,be}
(cherry picked from https://android-review.googlesource.com/q/commit:18c94565cdf7f1b359c64acd71c0b6b837d47ee3)
Merged-In: Iafa744633c7d757d4442528f35c85d9da352dd52
Change-Id: Iafa744633c7d757d4442528f35c85d9da352dd52