Update PropertySourcesPropertyValues so that collection values are only
added from a single PropertySource. Prior to this commit, given the
following:
PropertySource-A
list[0]=x
PropertySource-B
list[0]=y
list[1]=z
PropertySourcesPropertyValues would take `x` from A and `z` from B,
resulting in a binding of `[x,z]`. The updated code now returns the
more logical `[x]`.
Fixes gh-2611