* pr/10921:
  Polish

Closes gh-10921

See gh-10680

Further refine recursive binding rules so that Lists are supported when
the underlying source is iterable.

Close gh-10702

Refine the binder recursion rules introduced in commit f3373238 so
they only apply to Maps. Recursive List and Array binding is now no
longer allowed. Prior to this commit, binding a List that contained a
reference to itself would fail with a `StackOverflowException` if the
underlying property source was not iterable.

Fixes gh-10702

Update `CollectionBinderTests` with additional tests that cause a
`StackOverflowException` due to recursive list binding.

See gh-10702

Update `ApplicationPid` so that "canWrite" is only called for files
that already exist.

See gh-9922
Fixes gh-10784

* gh-10906:
  Polish Micrometer 1.0.0-rc.3 upgrade
  Upgrade to Micrometer 1.0.0-rc.3

Polish Micrometer 1.0.0-rc.3 upgrade changes.

Closes gh-10906

Upgrade to Micrometer 1.0.0-rc.3 and refactor existing
auto-configuration to align with updated APIs.

Note that Spring MVC instrumentation has now changed from an interceptor
to a Filter.

See gh-10906

Refactor `ReactiveWebApplicationContext` implementations to align closer
with the `WebApplicationContext` implementations defined in
Spring Framework.

The following classes are now provided:

  - `AnnotationConfigReactiveWebApplicationContext` -- A refreshable
    reactive web context with support for `@Configuration` classes.

  - `GenericReactiveWebApplicationContext` -- A non-refreshable reactive
    GenericApplicationContext.

  - `ReactiveWebServerApplicationContext` --  A non-refreshable reactive
    GenericApplicationContext with support for server discovery.

  - `AnnotationConfigReactiveWebServerApplicationContext` -- A
    non-refreshable reactive `GenericApplicationContext` with support
    for `@Configuration` classes and server discovery.

These classes roughly align to the following Servlet equivalents:

  - `AnnotationConfigWebApplicationContext` (Spring Framework)
  - `GenericWebApplicationContext` (Spring Framework)
  - `ServletWebServerApplicationContext` (Spring Boot)
  - `AnnotationConfigServletWebServerApplicationContext` (Spring Boot)

An additional `ConfigurableReactiveWebEnvironment` interface as also
been introduced, primarily for `@ConditionalOnWebApplication` to use.

Fixes gh-10852

Fixes gh-10866

Closes gh-10920

Closes gh-10919

Closes gh-10918

Closes gh-10917

Closes gh-10916

Closes gh-10915

Closes gh-10914

Closes gh-10913

Closes gh-10912

Closes gh-10911

Closes gh-10910

Closes gh-10909

Closes gh-10908

Closes gh-10905

This commit ensures that all errors handled by the
`DefaultErrorWebExceptionHandler` (Spring WebFlux error convetion
support) logs an error with request information and exception
stacktrace.

This is limited to errors that result in an HTTP 5xx error.
Exceptions that extend `ResponseStatusException` and set a non-5xx
status will not be logged.

Closes gh-10904

On WebSphere Liberty, the javax.validation package may be visible but
other javax.validation packages upon which it depends may not be
visible. This can lead to an incorrect assumption that the Bean
Validation API is available when, in fact, it is only partially
available.

Add an additional check for the availability of a class in the
javax.validation.bootstrap package to ensure that it's not just the
javax.validation package that's available.

Closes gh-10877

This commit enables HTTP/2 support for Tomcat and Undertow, for both
Servlet-based and Reactive applications.

Enabling the `server.http2.enabled` configuration flag is enough with
Undertow.

Tomcat has a few prerequisites:

* Tomcat 8.5 requires JDK8+ and the proper libtcnative version installed
on the host
* Tomcat 9.0.x requires JDK9+

Closes gh-10043

This commit adds a new configuration properties class for configuring
HTTP/2 protocol support.
By default, this protocol is disabled as enabling it requires several
manual changes:

* configuring a web server for proper TLS and ALPN support
* configuring a proper SSL certificate

See gh-10043

This commit applies the SSL configuration to the following reactive web
servers: Jetty, Tomcat, Undertow, Reactor Netty.

Closes gh-9431