[code-reflection] RFR: Quick hack to allow us to override codegen with annotation

[Gary Frost]

This allows us to override codegen (for experiments and to prototype cogegen fixes)

Add this to @CodeReflection annotated kernel entrypoints. 


@Kernel("""
     //kernel code
""")


If you need to add a new type (shared private mem) 

@TypeDef("""
     typedef struct SharedS32x256Array_s{
         int array[32];
     }SharedS32x256Array_t;
""" )


See PrefixSum as an example.

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Commit messages:
 - Quick hack to allow us to override codegen with annotation

Changes: https://git.openjdk.org/babylon/pull/622/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=622&range=00
  Stats: 135 lines in 4 files changed: 68 ins; 32 del; 35 mod
  Patch: https://git.openjdk.org/babylon/pull/622.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/622/head:pull/622

PR: https://git.openjdk.org/babylon/pull/622