zig: Add Windows support (#15197)

Release Notes:

- N/A

Currently Windows environments do not have a `shell_env`. This causes
the Zig extension to error when trying to call `worktree.shell_env()`
since extensions api isn't yet on `0.0.7` and thus not using wasm-host
`0.0.7` we need to only call for the shell env only on non-windows
systems. 0.0.7 and onward at the moment return a Result from
`shell_env()`. The binary path is also slightly different on windows.

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Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>