RFR: 8298730: Refactor subsystem_file_line_contents and add docs and tests [v2]

[Johan Sjölen]

On Wed, 14 Dec 2022 13:37:12 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> This puts `cpu_period` and `cpu_quota_val` next to each other, as they both read from `cpu.max` in opposite order (`"%*s %d"` and `"%1023s %*d"`). I think it improves readability, as it's not obvious why `%*d` is there otherwise. Still remove?
>
> Yes please, it's got nothing to do with this change. Feel free to move it in separate a RFE.

Alright, reverted.

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PR: https://git.openjdk.org/jdk/pull/11667