[code-reflection] RFR: PTX backend implementation for HAT [v2]

[Ruby Chen]

> Implemented a PTX backend for HAT kernel execution; PTX will run on machines with supporting Nvidia GPUs. Currently works for Squares and Mandel kernel examples.
> 
> Also starting to implement a BlackScholes kernel for HAT.

Ruby Chen has updated the pull request incrementally with one additional commit since the last revision:

  removing unnecessary optionals and appends

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Changes:
  - all: https://git.openjdk.org/babylon/pull/188/files
  - new: https://git.openjdk.org/babylon/pull/188/files/d2a941bd..e97e596d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=188&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=188&range=00-01

  Stats: 527 lines in 4 files changed: 323 ins; 43 del; 161 mod
  Patch: https://git.openjdk.org/babylon/pull/188.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/188/head:pull/188

PR: https://git.openjdk.org/babylon/pull/188