Closes gh-17478

Closes gh-17476

The `reactor-tools` dependency now brings a new Reactor Debug Agent
which instruments loaded classes for better Reactor stacktraces.
This commit removes the `spring.reactor.stacktrace-mode.enabled`
configuration property since the related Reactor Hook is about to be
removed.
As a replacement, we're introducing `spring.reactor.debug-agent.enabled`
which tells whether the Reactor Debug Agent should be loaded, given that
the `reactor-tools` dependency is available. This option is enabled by
default, since adding the dependency on classpath is a strong signal
already.

Fixes gh-17128

Prior to this commit, having the `spring-boot-starter-rsocket` and the
`jackson-dataformat-xml` dependencies on classpath would result in a
`ClassCastException` when the RSocket auto-configuration tries to
configure Jackson CBOR codecs for RSocket strategies.

This commit disables the Jackson XML support for the CBOR codec in
RSocket.

Fixes gh-17425

This commit uses native Reactor operators `Mono.fromCallable` and
`subscribeOn` for better performance and support.

Fixes gh-17452

* gh-17444:
  Use Assertions.contentOf() where possible

Closes gh-17444

See gh-17444

* gh-17473:
  Add Javadoc `@since` tags for new additional Tomcat connectors methods

Closes gh-17473

See gh-17473

* gh-17471:
  Remove folder that only contains package-info

Closes gh-17471

See gh-17471

Closes gh-17470

Fixes gh-17217

Closes gh-17467

Closes gh-17446

* gh-17462:
  Polish BatchAutoConfiguration

Closes gh-17462

See gh-17462

Closes gh-17466

Fixes gh-17465

* gh-17459:
  Polish Base64 usages

Closes gh-17459

See gh-17459

Closes gh-17463

Closes gh-17461

Closes gh-17460

Closes gh-17419

Closes gh-16663

* pr/17413:
  Polish

Closes gh-17413

See gh-17413

* pr/17448:
  Fix typo

Closes gh-17448

See gh-17448

Closes gh-17457

Closes gh-17445

Closes gh-17454

Closes gh-17451

Closes gh-17453

Closes gh-17449

* gh-17375:
  Polish "Add support for configuring a Batch-specific DataSource"
  Add support for configuring a Batch-specific DataSource

Closes gh-17375

See gh-17375

See gh-17375

* gh-17431:
  Remove references to archived spring-boot-issues repo

Closes gh-17431