ScriptNode : Cross-platform read-only check
ScriptNode : Cross-platform read-only check

- MSVC has deprecated `access`, we use `_waccess` as they recommend (the `w` prefix means the function expects a `wchar_t` pointer, which is what `boost::filesystem::path::c_str()` returns).
- The mode to check for is number 06, read and write, per https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/access-waccess?view=msvc-150
- This has the additional advantage of working with Linux ACLs.

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