Improve mmap handling of IO errors on WIN32.
Make MMAP gracefully handle IO errors on Windows by replacing the
mapping with zeros using a vectored exception handler when an
EXCEPTION_IN_PAGE_ERROR is raised. This is similar to how such errors
are handled on non-Windows platforms.
On Windows, this is implemented by first creating a placeholder
allocation and then mapping the file into it. When an error occurs, the
exception handler unmaps the file, keeping the placeholder intact, and
creates an anonymous mapping into it, after which execution can
continue.
Since some required functions don't exist on older Windows versions,
the error handling will only work on Windows 10, version 1803 or newer.
Ref !139739
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