Expand dist property checks to cover dists

Previously, only the dist property's nested properties were checked for
correctness. This change also checks the dists property's nested dist
structures and adds some tests to verify that the checks are run and
correctly report the location of the incorrect property even when it is
within a slice of dist structs.

Test: m nothing
Bug: 174226317
Change-Id: If5a19360e1e4c98ee3b5afc813e35349d1fc6f6f