Add platform info utilities

[nikolai-laevskii]

Adds shorthands for getting information about platform action is running on:

import { platform } from '@actions/core'

platform.platform // 'win32'
platform.arch // 'x64'
platform.isWindows // true
platform.isMacOS // false
platform.isLinux // false

const {
  name, // Microsoft Windows 11 Enterprise
  version, // 10.0.22621
} = await platform.getInfo()

Some checks are failing but not due changes. Tests and documentation are updated.

[nikolai-laevskii]

actions#1551