RFR: 8367413: Refactor types in Arguments::set_heap_size() [v4]

[Joel Sikström]

> Hello,
> 
> There are several integer types used when setting the heap size ergonomically in `Arguments::set_heap_size()`, such as julong, uint64_t and size_t. It's not clear if this code works as intended on a 32-bit VM with more than 4GB physical memory. There might be issues when converting to/from size_t and uint64_t that we don't handle properly. I suggest we should be more robust and have more control over transitions between potentially smaller types. 
> 
> Additionally, I've gone ahead and added comments which I think makes it easier to understand what's going on in this function. I've tried my best to leave the existing behavior unchanged, apart from type conversion.
> 
> Testing:
> * Oracle's tier1-8 on all Oracle supported platforms

Joel Sikström has updated the pull request incrementally with one additional commit since the last revision:

  Revert MaxRAM default removals, defer to future enhancement

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27224/files
  - new: https://git.openjdk.org/jdk/pull/27224/files/bd1f632e..2304c6aa

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27224&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27224&range=02-03

  Stats: 17 lines in 2 files changed: 17 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27224.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27224/head:pull/27224

PR: https://git.openjdk.org/jdk/pull/27224