[lworld] RFR: 8252506: [lworld] Multiple issues with C2's arraycopy intrinsic

[Tobias Hartmann]

This patch fixes multiple issues in C2's arraycopy/copyof/clone intrinsics:
- Flat inline type arrays containing oops might be copied without GC barriers.
- Missing membarrier in copyOf code at macro expansion
- We can often avoid flat/null-free checks by relying on the src <: dst subtype check
- We often know at parse time that a flat array does not contain oops and should make use of that information
- And more.. Hopefully the comments in the code are self-explanatory

Other changes:
- generic_arraycopy stub needs to handle flat/null-free inline type arrays
  - Bail if src is flat or dst is flat/null-free
  - Primitive array verification code is broken because array tag contains more bits
  - The "Load layout helper" comment needs adjustment as well but I'll wait with that until we've moved bits to the mark
    word
- C1 arraycopy intrinsic does not need to check arguments to generic_arraycopy stub (moved checks below)
- Added asserts and runtime verification code to catch issues earlier
- Added lots of test for all issues I've found and new IR matching rules to verify that all arraycopy optimizations work
  as expected
- Some refactoring

I've identified some remaining optimization opportunities and marked them with "TODO 8251971" in code and tests.

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

Commit messages:
 - 8252506: [lworld] Multiple issues with C2's arraycopy intrinsic

Changes: https://git.openjdk.java.net/valhalla/pull/178/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=178&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8252506
  Stats: 1052 lines in 11 files changed: 904 ins; 86 del; 62 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/178.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/178/head:pull/178

PR: https://git.openjdk.java.net/valhalla/pull/178