RFR: 8257901: ZGC: Take virtual memory usage into account when sizing heap [v3]

[Per Liden]

> MaxVirtMemFraction limits the amount of address space the GC should use for the heap. This is used by the heuristics in Arguments::set_heap_size() to select an appropriate default max heap size. However, that heuristic can select a max heap size that will not fit with ZGC, since ZGC uses additional address space (for multi-mapping and the virtual-to-physical ratio). As a result, if the address space is limited, and -Xmx is not specified, then ZGC might refuse to start with the error:
> 
> "Failed to reserve enough address space for Java heap"
> 
> I propose we abstract MaxVirtMemFraction to make it configurable for each GC, so that the heuristics in Arguments::set_heap_size() will pick a default max heap size that also works for ZGC.
> 
> Testing: Manual testing using different ulimit -v sizes.

Per Liden has updated the pull request incrementally with one additional commit since the last revision:

  Review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1696/files
  - new: https://git.openjdk.java.net/jdk/pull/1696/files/4370e0ed..eaaf4f97

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1696&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1696&range=01-02

  Stats: 9 lines in 3 files changed: 5 ins; 2 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1696.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1696/head:pull/1696

PR: https://git.openjdk.java.net/jdk/pull/1696