Release pages to OS when setting 0 label

This is a follow up patch of https://reviews.llvm.org/D88755.

When set 0 label for an address range, we can release pages within the
corresponding shadow address range to OS, and set only addresses outside
the pages to be 0.

Reviewed-by: morehouse, eugenis
Differential Revision: https://reviews.llvm.org/D89199