Closes gh-18824

Closes gh-18823

Closes gh-18822

Closes gh-18821

Closes gh-18820

Update `HealthEndpointConfiguration` to also include adapted reactive
health contributors when project reactor is on the classpath. Prior to
this commit, reactive contributors were only exposed in WebFlux
applications. This was a regression from Spring Boot 2.1 that we didn't
catch because all our own reactive contributors all have non-reactive
equivalents.

Closes gh-18805

This commit is a follow-up of a change in Spring Framework[1] to make
sure injection points that are expecting a specific bean by name use
a qualifier.

As a result of this change, MVC uses the dedicated MVC validator again
rather than the general one auto-configured by Spring Boot.

[1] https://github.com/spring-projects/spring-framework/issues/23887

Closes gh-18672

Closes gh-18802

Closes gh-18801

Closes gh-18800

Closes gh-18799

Closes gh-18797

Closes gh-18796

Closes gh-18795

Closes gh-18794

Closes gh-18793

Closes gh-18792

Closes gh-18791

Closes gh-18790

Closes gh-18789

Closes gh-18788

Closes gh-18787

Closes gh-18786

Closes gh-18785

Closes gh-18784

Closes gh-18783

Closes gh-18782

Closes gh-18781

Closes gh-18780

Closes gh-18779

Closes gh-18778

See gh-18744

See gh-18743

Closes gh-18649

* pr/18736:
  Polish contribution
  Polish

Closes gh-18736

See gh-18736