After an earlier rewrite, this flag works with all message types. So this expands its usage to some cases where we were using the `optional` flag for messages that are missing on Wine.
Some of the comments saying Wine is broken for not sending them turned out to be wrong - they're not always sent on Windows either - and in those cases the comments were removed.
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https://gitlab.winehq.org/wine/wine/-/merge_requests/5708
I was going to reimplement path resolution in ShellExecute, but half way through I realized that's very unnecessary.
Since what I wanted is a version of `PathResolve` that behaves differently _only_ for filespec paths, I ended up duplicating a lot of code, then I realized I can still pass filespec paths onto `PathResolve` and only deal with non-filespec paths.
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v2: shell32: Fix ShellExecute for non-filespec paths.
https://gitlab.winehq.org/wine/wine/-/merge_requests/5692