RFR: 8276550: Use SHA256 hash in build.tools.depend.Depend

[Aleksey Shipilev]

JDK-8182285 added the incremental build capabilities for modules, by hashing the APIs of each module.

The original change uses MD5, which is quite weak, and JDK-8214483 allows `MessageDigest` to have no MD5 implementation. This is the cause of some build failures when using a FIPS-compliant boot JDK that has no MD5 implementation. I suggest we switch to the latest available hash instead.

Additional testing:
 - [x] Linux x86_64 fastdebug build completes
 - [x] Linux x86_64 fastdebug build times do not regress

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Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/6231/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6231&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8276550
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6231.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6231/head:pull/6231

PR: https://git.openjdk.java.net/jdk/pull/6231