[VB6] cWebView2 — RC6-compatible WebView2 wrapper

This is a drop-in replacement of vbRichClient6's cWebView2 class, implemented in pure VB6 directly against the official Microsoft WebView2 COM API.

No RC6.dll dependency, no dependency on the WebView2 SDK typelib — the only redistributable is WebView2Loader.dll deployed next to the exe, targeting the Evergreen WebView2 Runtime installed on the client machine.

cheers,
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