[master] RFR: JDK-8301786: [Lilliput] Failing CompressedClassPointerEncoding.java

[Thomas Stuefe]

This fixes and expands runtime/CompressedOops/CompressedClassPointerEncoding.java.

Test had been broken by integration of [JDK-8294677](https://bugs.openjdk.org/browse/JDK-8294677), but to my embarrassment, I found that the test had never actually been finished, some vital checks were missing.

I fixed all that, clarified comments, and also changed the test to have multiple sub tests. I manually tested on x64 and aarch64.

On aarch64, I tried to test both `xor` and `movk` encoding modes but was unable to test latter - the lowest valid encoding base that would trigger `movk` mode is `0xa00_00000000`, and the kernel on my Raspi box is compiled for max. 39 bits for virtual user space addresses. That makes mapping at higher addresses fail. See comment in test.

There is more work to be done for aarch64: runtime/CompressedOops/CompressedClassPointerEncoding.java asserts. I opened https://bugs.openjdk.org/browse/JDK-8301880 to track that.

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Commit messages:
 - Fix Test

Changes: https://git.openjdk.org/lilliput/pull/72/files
 Webrev: https://webrevs.openjdk.org/?repo=lilliput&pr=72&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301786
  Stats: 321 lines in 1 file changed: 201 ins; 54 del; 66 mod
  Patch: https://git.openjdk.org/lilliput/pull/72.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/72/head:pull/72

PR: https://git.openjdk.org/lilliput/pull/72