pdl: Add canonical tests for body fields

Tag: #feature
Bug: 233340327
Test: atest pdl_tests pdl_rust_generator_tests_{le,be}
(cherry picked from https://android-review.googlesource.com/q/commit:84abde70629bab412cc6b2ec2df570d084a5a3bb)
Merged-In: I9701f2a9d41dd75b8280391b5d67f6c426a0a6c0
Change-Id: I9701f2a9d41dd75b8280391b5d67f6c426a0a6c0