RFR: 8287237: (fs) Files.probeContentType returns null if filename contains hash mark on Linux

[Brian Burkhalter]

Modify `sun.net.www.MimeTable.findByFileName(String)` to attempt to find the file extension in the entire file name if it is not found in the portion of the name preceding the optional fragment beginning with a hash (`#`).

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Commit messages:
 - 8287237: (fs) Files.probeContentType returns null if filename contains hash mark on Linux

Changes: https://git.openjdk.java.net/jdk/pull/8909/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8909&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287237
  Stats: 51 lines in 2 files changed: 37 ins; 2 del; 12 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8909.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8909/head:pull/8909

PR: https://git.openjdk.java.net/jdk/pull/8909