[vectorIntrinsics] RFR: Add utf8 decoding benchmarks [v2]

[Ludovic Henry]

> Following discussions on the mailing list, I'm submitting three benchmarks around UTF-8 decoding:
>  - decode: uses a while-loop based implementation currently in use in the JDK
>  - decodeVector: uses a lookup table with vector operations for 1-3 bytes characters
>  - decodeVectorASCII: uses a simple vector operation to accelerate parsing ASCII-only characters
> 
> We don't observe the expected speedups with either decodeVector and decodeVectorASCII, so these are, I think, good test cases to further develop the Vector API.

Ludovic Henry has updated the pull request incrementally with one additional commit since the last revision:

  Integrate @PaulSandoz improved code for decodeArrayVectorizedASCII

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Changes:
  - all: https://git.openjdk.java.net/panama-vector/pull/26/files
  - new: https://git.openjdk.java.net/panama-vector/pull/26/files/f738738e..e248178b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=26&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=26&range=00-01

  Stats: 9 lines in 1 file changed: 1 ins; 3 del; 5 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/26.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/26/head:pull/26

PR: https://git.openjdk.java.net/panama-vector/pull/26