RFR: Latest scope locals changes. [v2]

[Andrew Haley]

> In particular, support for Structured Concurrency, but also some JMH tests.

Andrew Haley has updated the pull request incrementally with two additional commits since the last revision:

 - Cleanup
 - Clean up tests

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/46/files
  - new: https://git.openjdk.java.net/loom/pull/46/files/ecf2160f..6edc5c2a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=46&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=46&range=00-01

  Stats: 47 lines in 6 files changed: 7 ins; 27 del; 13 mod
  Patch: https://git.openjdk.java.net/loom/pull/46.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/46/head:pull/46

PR: https://git.openjdk.java.net/loom/pull/46