RFR: 8337939: ZGC: Make assertions and checks less convoluted and explicit [v3]

[Joel Sikström]

> There are currently cases where calls to type converters are made only to assert whether the conversion is reasonable or not and then discarding the result. For example, to_zaddress(...) is used to check if the pointer passed to it is a valid zaddress or not, whilst discarding the result of the conversion.
> 
> Additionally, a call like oopDesc::is_oop(to_oop(o)) is convoluted since a similar check to is_oop() is already done inside to_oop(), which should be a separate operation in its entirety.
> 
> Asserts/checks in affected places should be separated so that assertion/checking can be explicitly made and not done more than necessary.
> 
> Tested with tiers 1-7 on linux64 and linux64-debug.

Joel Sikström has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' into zgc_assert_check_cleanup
 - Update copyright years
 - Fix zaddress parameter name
 - Update zPage.inline.hpp
 - 8337939: ZGC: Make assertions and checks less convoluted and explicit

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20478/files
  - new: https://git.openjdk.org/jdk/pull/20478/files/42044a86..426c4be6

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20478&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20478&range=01-02

  Stats: 7463 lines in 163 files changed: 2134 ins; 4812 del; 517 mod
  Patch: https://git.openjdk.org/jdk/pull/20478.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20478/head:pull/20478

PR: https://git.openjdk.org/jdk/pull/20478