Implement providing a custom AuthoritiesPopulator in ADLdapAuthProvider

[Haarolean]

Implemented a possibility to provide a custom AuthoritiesPopulator in ActiveDirectoryLdapAuthenticationProvider

Discussed in #4490

• I have extracted the existing implementation within loadUserAuthorities into a separate default AD populator, the same way it's done for non-AD LDAP AuthenticationProvider. Replaced a for with streams when collecting authorities;
• Mirrored existing constructors with a new parameter, keeping the old ones for back compatibility;
• Applied a few straightforward IDE-suggested fixes, let me know if you'd like me to revert them.

Resolves #4490

[jzheaux]

Thanks for the PR, @Haarolean! I've left some feedback inline.

[jzheaux]

@Haarolean, just one more thing, if you would please run:

./gradlew format && ./gradlew check

Then it will ensure that the code is following all of Spring Security's formatting standards. Thank you.

[Haarolean]

@Haarolean, just one more thing, if you would please run:

./gradlew format && ./gradlew check

Then it will ensure that the code is following all of Spring Security's formatting standards. Thank you.

Thanks, I've done checkFormat but didn't see there's another checkstyle.

[jzheaux]

Thanks, @Haarolean! This is now merged into main