Support java.nio.file Paths and FileSystems with nested jars

Add a `NestedFileSystemProvider` implementation so that the JDK's
`ZipFileSystem` can load content from nested jars and nested
directory entries.

Creating a `ZipFileSystem` may be a relatively expensive operation as
zip structures need to be parsed and in the case of directory entries
a virtual datablock nees to be generated on the fly. As such, we
install the `ZipFileSystem` as late as possible since in a typical
application it may never be needed.

This commit also tweaks Gradle and Maven plugins to ensure that the
service loader file is written to repackaged jars.

Closes gh-7161

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/resources/META-INF/services/java.nio.file.spi.FileSystemProvider

@@ -0,0 +1 @@
+org.springframework.boot.loader.nio.file.NestedFileSystemProvider