RFR: 8283335 : Add exists and readAttributesIfExists methods to FileSystemProvider [v4]

[Lance Andersen]

> Hi,
> 
> Please review the following patch which will:
> 
> - Enhance the java.nio.file.spi.FileSystemProvider abstract class to include the methods
> 
>   - public boolean exists(Path path, LinkOption... options)
>   - public <A extends BasicFileAttributes> A readAttributesIfExists(Path path, Class<A> type, LinkOption... options)
> 
> 
> This change allows for providers to provide optimizations when the file's attributes are not needed.
> 
> Mach5 tiers 1 - 3  run clean with this change
> 
> The CSR may be viewed at [JDK-8283336](https://bugs.openjdk.org/browse/JDK-8283336)
> 
> 
> Best,
> Lance

Lance Andersen has updated the pull request incrementally with one additional commit since the last revision:

  Updated tests based on feedback

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/9249/files
  - new: https://git.openjdk.org/jdk/pull/9249/files/6ef8bc1f..63b97ce3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9249&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9249&range=02-03

  Stats: 293 lines in 3 files changed: 156 ins; 133 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/9249.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9249/head:pull/9249

PR: https://git.openjdk.org/jdk/pull/9249