The changes made in 919d0c61 meant that the value of
spring.profiles.active or spring.profiles.include was only processed
when a single property source, the property source for the config file
being read, was available. This meant that any placeholders in those
values would only be resolved against properties in the configuration
file rather than against the entire environment.

This commit updates the binding process so that placeholder resolution
is not performed during binding against a single configuration file.
Once binding has completed, the bounds values are post-processed to
resolve and placeholders that they may contain.

The two-step process described above is used in preference to binding
against the whole environment. This avoids a problem with profiles
that are active or included by property sources in the environment
being processed repeatedly.

Closes gh-8234