Provide a hashcode implementation for `ConfigurationPropertyName` so
that instances can be stored in Map without them all ending up in the
same bucket.

See gh-20625

Add a test to ensure that a large number of property sources that each
contain many items can perform well.

See gh-20625

Remove the recently added slash restriction since Spring Cloud
Config Server needs to support names with slashes.

See gh-21217

Closes gh-21352

Closes gh-21351

Closes gh-21342

Closes gh-21349

Closes gh-21348

Closes gh-21346

Closes gh-21344

Closes gh-21213

Closes gh-21343

Prior to this commit, the property was a Boolean with a null default.
If it was explicitly set by the user, a context customizer would use
that value to set it on the context. However, if it was not set, the default
wouldn't be tomcat's default but `false` because it was explicitly set to
`false` in `TomcatServletWebServerFactory`. This commit defaults the property
itself to `false` so that the default is more obvious to the user.

Fixes gh-20796

Fix the `SystemEnvironmentPropertyMapper.isAncestorOf` implementation
to convert names based on their dashed form and to silently ignore
any invalid results.

Closes gh-14479

Closes gh-21341

Fixes gh-20759

The warnings will be addressed by gh-20759. CreateBootStartScripts
must be excluded from the classes that are validated by the
ValidatePlugins task. It is invalid, but only for Gradle 6.4. gh-20759
will cause it to only be used with Gradle 6.3 and earlier.

See gh-21329

Closes gh-21340

Closes gh-21339

Closes gh-21338

Closes gh-21337

Closes gh-21336

Closes gh-21335

Closes gh-21334

Closes gh-21333

Closes gh-21332

Closes gh-21331

Closes gh-21330

Closes gh-21329

Closes gh-21327