Supported platform of some fields in process.resourceUsage

[srknzl]

Affected URL(s)

https://nodejs.org/api/process.html#processresourceusage

Description of the problem

According to the documentation:

sharedMemorySize [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to ru_ixrss but is not supported by any platform.
unsharedDataSize [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to ru_idrss but is not supported by any platform.
unsharedStackSize [<integer>](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type) maps to ru_isrss but is not supported by any platform.

I did not understand why they are not supported by any platform. Did you mean is not supported by all platforms ? If it is not supported by any platform, why do we have it?

[mscdex]

This question was asked in the original PR here. In short: we have them in case they are used by a platform in the future.

[srknzl]

Thank you

[srknzl]

@mscdex is it reasonable to add this to documentation in case someone asks it again?