Update RelaxedDataBinder so that multiple overlapping nested property
names can be bound to a Map.

Prior to this commit, properties of the following form could not be
bound to Maps:

  foo: baz
  foo.bar: spam

This was due to BeanWrapperImpl throwing an InvalidPropertyException
when binding `map[foo][bar]` because `foo` is already bound to `baz`.

The updated code now detects such cases and instead uses the binding
property `map[foo.bar]`.

Fixes gh-2610