Investigate possibility of sqlite3_load_extension

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@ericsink Would it be possible to add sqlite3_load_extension to SQLitePCLRaw?

Originally posted by @bricelam in dotnet/efcore#26220 (comment)

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Maaaybe.

I'll take a fresh look at this. IIRC, I omitted the function (years ago) because it caused problems with native SQLite libs where it had been compiled out and where AOT was in play. Specifically, I think it was iOS and bundle_green that was complaining.

But I haven't revisited the matter in a long time, so it's worth checking to see what could be done.

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I'm guessing this can be closed, as the following change by @bricelam makes use of this feature, apparently successfully:

dotnet/efcore#28903