RFR: 8310675: Fix -Wconversion warnings in ZGC code [v2]

[Joel Sikström]

> Fixed `-Wconversion` warnings in ZGC code, either by adding an explicit type cast, changin the type of the variable or calling an equivalent method with other types. The largest change is the addition of `ZStatDurationSample`, which typecasts `Tickspan::value()` to a `uint64_t` and calls `ZStatSample` to make the code more readable.
> 
> I isolated the `-Wconversion` warnings for ZGC by adding the flag to clangd and displaying the errors in my IDE and going through each file directly associated with ZGC one by one.
> 
> Tested with tiers 1-3.

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 two additional commits since the last revision:

 - Merge branch 'master' into JDK-8310675
 - 8310675: Fixed -Wconversion warnings in ZGC

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20406/files
  - new: https://git.openjdk.org/jdk/pull/20406/files/5c3206cd..2b28a82f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20406&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20406&range=00-01

  Stats: 13259 lines in 509 files changed: 6983 ins; 4162 del; 2114 mod
  Patch: https://git.openjdk.org/jdk/pull/20406.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20406/head:pull/20406

PR: https://git.openjdk.org/jdk/pull/20406