* hid: Rewrite shared memory management
This entirely rewrite our ancient (and original) HID shared memory
interface to be more usable and accurate.
HID update logics were updated to reflect those changes but should work
still the same way it previously did.
This need heavy testing just in case to avoid possible regressions.
* Silence warnings
* Address gdkchan's comments
* Address Ac_K's comments
* Address one missing nit
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