RFR: Split out ContinuationEntry and ContinuationWrapper classes

[Coleen Phillimore]

Moved ContinuationEntry and ContinuationWrapper to their own files.
There's a bit of inconsistency because 3 ContinuationEntry functions are in ContinuationHelper_cpu.inline.hpp - maybe we should have continuationEntry_cpu.inline.hpp files for just the three.
I'd like to change the name ContinuationEntry to ContinuationAnchor or ContinuationFrameAnchor but want to study how that would look a bit more first.
Tested with other platforms and testing with loom-tier1 as sanity.

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Commit messages:
 - Minor changes to keep platforms consistent.
 - Add ContinuationEntry and ContinuationWrapper classes in separate files.

Changes: https://git.openjdk.java.net/loom/pull/145/files
 Webrev: https://webrevs.openjdk.java.net/?repo=loom&pr=145&range=00
  Stats: 1479 lines in 37 files changed: 657 ins; 789 del; 33 mod
  Patch: https://git.openjdk.java.net/loom/pull/145.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/145/head:pull/145

PR: https://git.openjdk.java.net/loom/pull/145