Fixes gh-6229

Fix issue where FixedAuthoritiesExtractor would fail to obtain standard
item from the map because an incorrect key was used.

Fixes gh-6396

See gh-4313

Revert the previous upgrade due to the MCOMPILER-271 issue.

Fixes gh-6391

See gh-6390

Add a dedicated section to explain how YAML lists are merged.

See gh-4313

Update PropertySourcesPropertyValues so that source detection logic for
collection values also considers complex types. Prior to this commit
properties of the following form were processed correctly:

	PropertySource-A
	  list[0]=x

	PropertySource-B
	  list[0]=y
	  list[1]=z

But properties of the form were not:

	PropertySource-A
	  list[0].name=x

	PropertySource-B
	  list[0].name=y
	  list[1].name=z

Fixes gh-4313
See gh-2611

Closes gh-6346

Fixes gh-6387

Closes gh-6333

Closes gh-6339

Previously, one SpringApplicationAdminMXBeanRegistrar was created
per context. When there was more then one context this would result
in a javax.management.InstanceAlreadyExistsException being thrown
as an attempt was made to register the MBean more than once.

This commit updates SpringApplicationAdminJmxAutoConfiguration so
that the registrar is only created when there's no such existing bean
in the context hierarchy.

Closes gh-6378

- Call get rather than containsKey then get
- Only call putIfAbsent after get has returned null to avoid unnecessary
  object creation

Closes gh-6382

Closes gh-6377

* gh-6379:
  Improves metrics performance by not guarding map.get

ConcurrentHashMap implements `containsKey` with `get`. By removing a
redundant call to `containsKey`, we guarantee better performance in our
counter services.

The geek inside measured this with JMH, and found under 4 threads of
contention, throughput on this check was 40% higher in success case.

Benchmark                                  Mode  Cnt     Score     Error   Units
TestBenchmarks.containsKeyAndGet_success  thrpt   30   432.389 ±  20.616  ops/us
TestBenchmarks.get_success                thrpt   30   606.789 ±  10.848  ops/us

Closes gh-6379

* gh-6381:
  Upgrade to Thymeleaf 2.1.5.RELEASE

Closes gh-6381

Closes gh-4393

Previously, if there was a hierarchy of SpringApplications, the admin
MBean would report that the application was ready as soon as any
application in the hierarchy was ready. This could lead to a client
trying to query a property in the environment before it's available.

This commit updates the MBean registrar to that the MBean only reports
that the application is ready when the context that contains the
registrar has refreshed and fired its ApplicationReadyEvent.

Closes gh-6362

* pr/6374:
  Polish

Closes gh-6374

Update SpringBootTestContextBootstrapper to consider the
`@WebAppConfiguration` annotation and use sensible resourceBasePath
defaults.

Fixes gh-6371

Use a custom GeneratorStrategy to fix the package tangles that jOOQ
creates by default.

Fixes gh-6372

Relocate `SpringBootPlugin` to fix a package tangle.

Fixes gh-6355

Closes gh-6360

Closes gh-6369

Closes gh-6008

Closes gh-6357