Closes gh-6288

Closes gh-6287

Closes gh-6286

Closes gh-6285

Closes gh-6284

Closes gh-6283

Closes gh-6282

Closes gh-6281

Closes gh-6280

Closes gh-6279

Closes gh-6278

Closes gh-6277

* pr/6304:
  Remove duplicate property reference

Closes gh-6304

See gh-6261

Closes gh-6275

Closes gh-6276

Closes gh-6276

Closes gh-6274

Closes gh-6273

Closes gh-6271

Closes gh-6270

Closes gh-6269

Closes gh-6268

Closes gh-6267

Closes gh-6266

Closes gh-6265

* gh-6241:
  Add an accessor for webEnvironment to SpringApplication

Closes gh-6241

Where possible, code that previously synchronized on this (or on the
class in the case of static methods) has been updated to use an
internal monitor object instead. This allows the locking model that's
employed to be an implementation detail rather than part of the
class's API.

Classes that override a synchronized method continue to declare
the overriding method as synchronized. This ensures that locking
is consistent across the superclass and its subclass.

Closes gh-6262

Closes gh-6263

Update AuditEventRepository to restore support for `null` arguments and
explicitly Javadoc their meaning.

See gh-5854

Closes gh-6257

Closes gh-6253

Previously, Log4J2LoggingSystem used ResourceUtils.isFileURL(URL) to
check that the URL of the configuration was suitable for accessing as a
File. Unfortunately, this fails when the URL’s protocol is vfs or
vfsfile as both return true and then fail when the URL is subsequently
passed into ResourceUtils.getFile(URL).

This commit switches to checking that the URL’s protocol is file,
the only protocol that will allow getFile(URL) to succeed.

Closes gh-6246