[vectorIntrinsics] RFR: Conversion test refactor

[Paul Sandoz]

Refactor the conversions tests:

- simplify the signature of the kernels

- improve the performance (hoisting out expected result from main loop)

- ensure contents of actual and expected arrays are compared.

The core change is to `AbstractVectorConversionTest.java` with many formulaic changes to the tests. A follow on change can be proposed to reduce the number of methods in each test by using a provider providing a cross product of values under test.

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Commit messages:
 - Refactor reinterpret_kernel
 - Merge remote-tracking branch 'upstream/vectorIntrinsics' into conversion-test-refactor
 - Refactor tests to be faster.

Changes: https://git.openjdk.java.net/panama-vector/pull/21/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=21&range=00
  Stats: 22701 lines in 6 files changed: 115 ins; 14633 del; 7953 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/21.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/21/head:pull/21

PR: https://git.openjdk.java.net/panama-vector/pull/21