Add sqlite3_wasm_vfs_create_file() to replace Emscripten's FS.createDataFile() in...

Add sqlite3_wasm_vfs_create_file() to replace Emscripten's FS.createDataFile() in a (mostly) VFS-agnostic way. Add a test for worker1's export (to bytearray) support. Re-add worker1 open-from-bytearray using sqlite3_wasm_vfs_create_file() but it's untested (requires a new interactive test app or maybe reconsideration).

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