[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/go-sqlite3/vfs/shm_other.go

@@ -0,0 +1,21 @@
+//go:build !(darwin || linux) || !(amd64 || arm64 || riscv64) || sqlite3_flock || sqlite3_noshm || sqlite3_nosys
+
+package vfs
+
+// SupportsSharedMemory is false on platforms that do not support shared memory.
+// To use [WAL without shared-memory], you need to set [EXCLUSIVE locking mode].
+//
+// [WAL without shared-memory]: https://sqlite.org/wal.html#noshm
+// [EXCLUSIVE locking mode]: https://sqlite.org/pragma.html#pragma_locking_mode
+const SupportsSharedMemory = false
+
+// NewSharedMemory returns a shared-memory WAL-index
+// backed by a file with the given path.
+// It will return nil if shared-memory is not supported,
+// or not appropriate for the given flags.
+// Only [OPEN_MAIN_DB] databases may need a WAL-index.
+// You must ensure all concurrent accesses to a database
+// use shared-memory instances created with the same path.
+func NewSharedMemory(path string, flags OpenFlag) SharedMemory {
+	return nil
+}