RFR: 8291945: Add OSInfo API for static OS information

[David Holmes]

On Thu, 4 Aug 2022 23:18:35 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> As suggested by @tstuefe in the review of #9600, many of the `os` APIs simply return a value that was initialized during VM start up. E.g., `os::vm_page_size()`. I have added a new class `OSInfo` for managing such info
> 
> - Simplifies the per-OS implementation
> - Make the "init-only-once" check consistent
> - In some cases, the simpler `OSInfo` class can be used in lieu of the more complex `os` class. This improves HotSpot build time (e.g., relocInfo.hpp).
> 
> Note: I moved only 2 fields in this PR as a first step. If this works well I plan to move more fields in the future.

Marked as reviewed by dholmes (Reviewer).

Okay I think it would be good to switch to the OSInfo API in the future, so that we reduce the scope of os even further and more clearly delineate an API to request services from the OS, and a simple query API for the OS.

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PR: https://git.openjdk.org/jdk/pull/9758