LibCore: Port MappedFile to Windows

[stasoid]

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[stasoid]

Marked this as draft because it looks like we better off using mman vcpkg package after all, as suggested by @zacuke. Core::System::mmap cannot be used in AK/BumpAllocator.h because AK should not depend on LibCore. There is a slight caveat that mmap from mman does not support MAP_PRIVATE, but this is not a problem in our case.

[ADKaster]

If we can't create MAP_PRIVATE | MAP_ANONYMOUS mappings, then an mman wrapper package doesn't seem particularly useful. Unless I'm missing something, we would want to use VirtualAlloc for BumpAllocator. In the ladybird codebase, BumpAllocator is only used by LibRegex. The only other place we use MAP_ANONYMOUS is in the LibGC heap allocator.

It's definitely true that nobody in Ladybird is using a read-write Core::MappedFile, so a read-only mapping for those use cases is just fine.

[stasoid]

MAP_PRIVATE | MAP_ANONYMOUS is not a problem either because:

    // Anonymous mapping returned by this function is effectively always private because
    // the only way to share it is via the handle, which is immediately closed after MapViewOfFile.
    // Hence:
    // * shared anonymous is not supported
    // * private anonymous does not need to use copy-on-write

(mman mmap closes the map handle too)