RFR: 8315024: Vector API FP reduction tests should not test for exact equality

[Gergö Barany]

Certain floating point reduction operations in the Vector API are allowed to introduce rounding errors. Adjust the corresponding tests to allow a small relative error when comparing the operation's result to the expected value. Also, add a new generator `double[i / 10.0 + 0.1]` to test floating point operations with somewhat more interesting input data.

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Commit messages:
 - 8315024: Vector API FP reduction tests should not test for exact equality

Changes: https://git.openjdk.org/jdk/pull/16024/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16024&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315024
  Stats: 463 lines in 13 files changed: 423 ins; 0 del; 40 mod
  Patch: https://git.openjdk.org/jdk/pull/16024.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16024/head:pull/16024

PR: https://git.openjdk.org/jdk/pull/16024