[code-reflection] Integrated: initial prototype of prefix sum experiment

[Gary Frost]

This will be a good demonstrator for recent  array view and local memory work. 

Also the basis for a reduction based violajones implementation. 

I also added matmul.iml so we can view matmul in intellij project

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Commit messages:
 - initial prototype of prefix sum experiment

Changes: https://git.openjdk.org/babylon/pull/593/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=593&range=00
  Stats: 341 lines in 3 files changed: 341 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/babylon/pull/593.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/593/head:pull/593

PR: https://git.openjdk.org/babylon/pull/593