[code-reflection] RFR: [hat][proposal] Adding notion of local thread ids and local group sizes int HAT

[Juan Fumero]

This PR extends the `KernelContext` API to access local thread ids and group sizes. 

It keeps compatibility with the prev. API, thus, it maintains the `kernelcontext.x` and `kernelcontext.maxX` thread accessors. However, we might remove this in near future in favour for the kernelContext.gix and `kernelcontext.gsx`. 
This is just a proposal.

Simple example:


@CodeReflection
    private static void assign(@RO KernelContext context, @RW S32Array arrayA, @RW S32Array arrayB, @RW S32Array arrayC) {
        int gix = context.gix;
        int lix = context.lix;
        int lsx = context.lsx;
        int bsx = context.bsx;
        arrayA.array (gix, lix);    // Store local thread id
        arrayB.array(gix, lsx);    // Store local size
        arrayC.array(gix, bsx);   // Store thread block id
    }


How to test:



# For OpenCL
 java -cp job.jar hat.java exp ffi-opencl $@                                                                                            
 
# For CUDA                                                                                                                                        
 java -cp job.jar hat.java exp ffi-cuda $@ 


Still a draft PR until double checking with the CUDA backend.

-------------

Commit messages:
 - [hat] Remove old kernel context code
 - [hat] CUDA thread-block and block dispatch fixed
 - [hat] roll back to plain kernelContext in the C99 kernel (ocl)
 - [hat] Definition of local ids and local groups
 - [hat] comment for future codegen of the kernelContext
 - ComputeContext names simplified
 - Merge branch 'code-reflection' into hat/api/local
 - [hat] fix field ordering to process local/global groups and local thread ids
 - [hat] Sample local ids documented
 - [hat] jextracted codegen fixed
 - ... and 12 more: https://git.openjdk.org/babylon/compare/bb4f7ff8...0044f814

Changes: https://git.openjdk.org/babylon/pull/527/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=527&range=00
  Stats: 634 lines in 20 files changed: 469 ins; 95 del; 70 mod
  Patch: https://git.openjdk.org/babylon/pull/527.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/527/head:pull/527

PR: https://git.openjdk.org/babylon/pull/527