Closes gh-23497

Closes gh-23492

Closes gh-23494

Closes gh-23493

Previously, we configured embedded Tomcat in such a way that no TLD
scan patterns were configured. This differed from a standalone
Tomcat installation where 4 patterns are configured that take
precedence over some of the skip patterns. The missing scan patterns
resulted in the skip patterns preventing the discovery of Log4j2's
TLDs.

This commit updates TomcatServletWebServerFactory to configure the
same four scan patterns as standalone Tomcat configures by default.

Fixes gh-23302

Previously, the web environment configured on `@SpringBootTest` was not
part of the context cache key. As a result, two test classes that has
identical configuration other than one using a MOCK web environment and
the other using a DEFINED_PORT web environment would share a context
when they should not do so. Classes that use MOCK and RANDOM_PORT were
not affected as the use of RANDOM_PORT results in a property for the
port being added to the environment.

This commit adds a new ContextCustomizer, SpringBootTestWebEnvironment,
that is used to capture the `webEnvironment` from `@SpringBootTest`
and use it in its hashCode and equals implementations. This fixes the
problem as all context customizers are evaluated when determing the
equality of two context cache keys.

Fixes gh-23085

Closes gh-23471

Closes gh-23469

Closes gh-23473

Closes gh-23468

* pr/23459:
  Fix link to Log4j's JDK Logging Adapter in reference documentation

Closes gh-23459

See gh-23459

See gh-22983

This commit rework the tip on locating templates when running the app
in the IDE. Using classpath* should not change anything as this won't
make a difference without a pattern in the path.

Closes gh-23068

Closes gh-23447

* pr/23445:
  Fix multi-release JAR test on JDK 15

Closes gh-23445

Backport of 54f93e9b

See gh-23445

Closes gh-23443

Update `HandlerFunctionDescription` so that it will work with JDK 15.

Closes gh-23442

See gh-23433

See gh-23440

Make `StringSequence.isEmpty()` public for compatibility with JDK 15.

Closes gh-23440

Closes gh-23439

See gh-23433

Closes gh-23433

See gh-22983

Previously LOG_LEVEL_PATTERN and LOG_DATEFORMAT_PATTERN were not
consumed as system properties in log4j2.xml and log4j2-file.xml. As a
result, the logging.pattern.level and logging.pattern.dateformat
configuration properties, which are translated into the
LOG_LEVEL_PATTERN and LOG_DATEFORMAT_PATTERN system properties
respectively had no effect.

This commit updates the log4j2.xml and log4j2-file.xml config files to
consume LOG_LEVEL_PATTERN and LOG_DATEFORMAT_PATTERN as system
properties. When the system property is not set, the configuation falls
back to the default values specified in the config files. Tests for
both log4j2.xml and log4j2-file.xml to verify the behaviour have also
bean added.

Fixes gh-22983

Closes gh-23425

* gh-23418:
  Polish "Add note about Kotlin main class name"
  Add note about Kotlin main class name

Closes gh-23418

See gh-23418

See gh-23418

Closes gh-23416

Closes gh-23415

Previously, spring.flyway.init-sqls was only applied to Flyway's
configuration if Flyway was being configured to create the DataSource.
If Flyway was being configured to use an existing DataSource, init-sqls
was not applied. This is a hangover from when the init SQLs support was
introduced. At that time, Flyway only supported SQL to initialize the
connection when it was creating the DataSource. Flyway 5.2 added init
SQL support no matter how Flyway's DataSource was configured.

This commit updates FlywayAutoConfiguration to always apply the
init-sqls property to Flyway's configuration. The property's
documentation does not describe the current limitation so this change
should align the behaviour with what the documentation leads people to
expect.

Fixes gh-23392

Fixes gh-23402