RFR: 8274883: (se) Selector.open throws IAE when the default file system provider is changed to a custom provider

[Maxim Kartashev]

The gist of the problem: when a file system is specified via `-Djava.nio.file.spi.DefaultFileSystemProvider`, a call to `SelectorProvider.provider().openSelector()` ends with a throw on Windows.

There are two distinct components to the problem:

1. `ExceptionInInitializerError` is thrown during the static initialization of the `UnixDomainSockets.UNNAMED` field even though it isn't used on this code path (see `UnixDomainSocketAddress.of()` that throws `IllegalArgumentException` if invoked on a path from a non-default file system). 
This is fixed by lazy-initializing the static member `UNNAMED` of `UnixDomainSockets` so that this initialization doesn't throw unless actually used.

2. `IllegalArgumentException` is thrown by `UnixDomainSocketAddress.of()`  later on when `ServerSocketChannel` tries to use Windows version of `PipeImpl` and its method `createListener()` specifically. That `PipeImpl` probes for the availability of Unix Domain Sockets by trying to bind to a unique temporary name. That call throws `IAE` when a non-default Java file system is installed while the probing code (`PipeImpl.createListener()`) only expects `UnsupportedOperationException` or `IOException`.
The fix is to re-throw `UOE` instead of `IAE` in `UnixDomainSockets.genrateTempName()`. This is more consistent with the definition of the exception purpose ("requested operation is not supported"). So with this change, a loopback network socket will be used to implement a pipe on a non-default Java file system. Also, pipes do not rely on the default Java file system on other platforms (Linux, MacOS) as well.

Tested by running `jtreg:test/jdk/java/nio` on Window, MacOS, and Linux.

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Commit messages:
 - 8274883: (se) Selector.open throws IAE when the default file system provider is changed to a custom provider

Changes: https://git.openjdk.java.net/jdk/pull/6722/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6722&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274883
  Stats: 50 lines in 3 files changed: 46 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6722.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6722/head:pull/6722

PR: https://git.openjdk.java.net/jdk/pull/6722