we still need that targets file for the pinvoke anycpu cases.  not done yet.
for anycpu/pinvoke nuget targets files, copy all the native sqlite3 dlls into the output directory, each into a subdir named for its cpu.  need the C# pinvoke layer to load the correct one at runtime.  need non-anycpu versions to continue to work the old way, even though no such builds are actually copied into a nuget pkg at this time.  need android and unified to get a targets file that is customized for their situation, supporting the optional use of the latest version of sqlite bundled as well.  something similar for net45, which also needs special support for non-windows mono.
copy some code (ASL2) from vnet aspnet/DataCommon.SQLite to do the LoadLibrary trick so that anycpu pinvoke can determine the sqlite3 dll at runtime
fixes to the LoadLibrary code, which isn't actually being used yet