`windows-notifyicon`: Add ability to provide HICON manually

NotifyIcon appears to require an icon file on disk. I'd like to instead handle that part and hand NotifyIcon a handle to an icon I've loaded via other means. This handle may also be shared (see LR_SHARED) and not Owned, so should not be destroyed.

For example, I may want to call `LoadLibraryEx(... | LOAD_LIBRARY_AS_IMAGE_RESOURCE)` > `LoadIconWithScaleDown` > `HICON` and perhaps `NotifyIcon::new(icon_handle)...`.

Start by locating the windows-notifyicon entry point and the NotifyIcon::new API that currently accepts an icon file. Trace how the HICON is stored and released, including the shared-handle case described with LR_SHARED. Done means callers can provide an HICON directly without NotifyIcon destroying a handle it does not own.

Written by the indexing model from the issue text.