Develop custom ApplicationEnvironment implementation

[philwebb]

We could improve quite a few things if we developed our own Environment implementation rather than relying on StandardEnvironment.

For example, whilst trying to fix #24890 I discovered it's impossible for us to totally filter out spring.profiles.active properties due to AbstractEnvironment.doGetActiveProfiles().

It might also allow us to remove ConfigurationPropertySourcesPropertySource and possibly fix #17400

[chaundhyan]

@philwebb
Have you started working on this?
If not, would you assign this enhancement to me?
Thanks

[wilkinsona]

Thanks for the offer, @chaundhyan. @philwebb is already working on this with with some changes to Spring Framework (see spring-projects/spring-framework#26461 and spring-projects/spring-framework#26462 for details).