windows: expose reparse buffer types

[tomgr]

These are needed for interacting with reparse buffers on Windows.
Searching on github reveals a lot of repositories that have copied these
types, so it would make sense to export them directly.

This also copies a method on SymbolicLinkReparseBuffer from
go/src/internal/syscall/windows/reparse_windows.go to ease interacting
with symbolic links.

[gopherbot]

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Thomas Gibson-Robinson:

Patch Set 1:

(1 comment)

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