Dedup path properties across property structs

Listing a property in multiple property structs would cause it to
add multiple dependencies with the same dependency tag, which would
trip the panic in getDirectDepInternal when calling
PathForModuleSrc.  Dedup the properties with the android:"path"
struct tag across all property structs.

Test: path_properties_test.go
Change-Id: Ib6c0e7789443d340ee7551721df0135c5ee64c0f