RFR: 8266891: Provide a switch to force the class space to a specific location [v2]

[Thomas Stuefe]

> To test compressed Klass pointer encoding and other metaspace interna, it would be nice to be able to force location of the class space to a specific location. This would help with analysis of problems like JDK-8261552 or JDK-8265705 - errors in Klass* encoding/decoding which managed to stay unnoticed for an astonishingly long time.
> 
> For simplicity, it would be sufficient to only have this ability if CDS is disabled (Xshare=off), since CCS allocation is tied to CDS location otherwise and that would be more diffictult to disentangle.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  Feedback Coleen

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3969/files
  - new: https://git.openjdk.java.net/jdk/pull/3969/files/532a7287..2d962a24

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3969&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3969&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3969.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3969/head:pull/3969

PR: https://git.openjdk.java.net/jdk/pull/3969