(fs) Remove FileSystem support for resolving against a default directory (chdir configuration)

Early execution of UnixNativeDispatcher is avoided if support for resolving against a specified filesystem default directory is removed. This entails removing the undocumented property “sun.nio.fs.chdirAllowed” and setting the default directory to the value of the “user.dir” property.

Previous description:

When creating a UnixFileSystem, by default we make syscalls to determine the value of needToResolveAgainstDefaultDirectory. The value of this field could potentially be calculated lazily.

Doing so removes early use of UnixNativeDispatcher, which defers loading of the nio library and reduces the number of classes we load on minimal JVM execution by up to 13

A similar startup gain can be seen when setting -Dsun.nio.fs.chdirAllowed=true