[code-reflection] RFR: [hat] Float2 supported

[Juan Fumero]

This PR adds `float2` in the API to generate 2 float instructions for OpenCL and CUDA backends. 

How to test?


HAT=SHOW_CODE java -cp hat/job.jar hat.java test ffi-opencl hat.test.TestFloat2
HAT=SHOW_CODE java -cp hat/job.jar hat.java test ffi-cuda hat.test.TestFloat2

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Commit messages:
 - [hat] Add tests for float2 similar to float4
 - [hat] Adding float2 work

Changes: https://git.openjdk.org/babylon/pull/666/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=666&range=00
  Stats: 840 lines in 9 files changed: 829 ins; 6 del; 5 mod
  Patch: https://git.openjdk.org/babylon/pull/666.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/666/head:pull/666

PR: https://git.openjdk.org/babylon/pull/666