Use native assets experiment to compile sqlite3

[simolus3]

Use the --native-assets experiment to compile sqlite3 without using platform-specific build scripts (like sqlite3_flutter_libs).

We still need to support downloading sqlite3 from an URL as a build mode. It would also be nice to be able to pass additional compile flags or remove to some of the OMITs we're applying.

Another todo: We're now able to avoid some of the copies when binding blobs and strings by directly passing the list.