RFR: 8286401: Address possibly lossy conversions in Microbenchmarks

[Claes Redestad]

#8599 would add a new warning. This address the conversions in the microbenchmark component by means of making the types precise or adding explicit casts. There's quite a few changes in the ByteBuffers benchmarks, but the real change is in the template as these are generated.

I've run through a subset of the affected benchmarks and verified that the results are either neutral or improve somewhat (seem to be the case in a few of the ByteBuffer micros).

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Commit messages:
 - 8286401: Address possibly lossy conversions in Microbenchmarks

Changes: https://git.openjdk.java.net/jdk/pull/8654/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8654&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286401
  Stats: 166 lines in 12 files changed: 0 ins; 0 del; 166 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8654.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8654/head:pull/8654

PR: https://git.openjdk.java.net/jdk/pull/8654