[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/memdb/api.go

@@ -0,0 +1,68 @@
+// Package memdb implements the "memdb" SQLite VFS.
+//
+// The "memdb" [vfs.VFS] allows the same in-memory database to be shared
+// among multiple database connections in the same process,
+// as long as the database name begins with "/".
+//
+// Importing package memdb registers the VFS:
+//
+//	import _ "github.com/ncruces/go-sqlite3/vfs/memdb"
+package memdb
+
+import (
+	"sync"
+
+	"github.com/ncruces/go-sqlite3/vfs"
+)
+
+func init() {
+	vfs.Register("memdb", memVFS{})
+}
+
+var (
+	memoryMtx sync.Mutex
+	// +checklocks:memoryMtx
+	memoryDBs = map[string]*memDB{}
+)
+
+// Create creates a shared memory database,
+// using data as its initial contents.
+// The new database takes ownership of data,
+// and the caller should not use data after this call.
+func Create(name string, data []byte) {
+	memoryMtx.Lock()
+	defer memoryMtx.Unlock()
+
+	db := &memDB{
+		refs: 1,
+		name: name,
+		size: int64(len(data)),
+	}
+
+	// Convert data from WAL to rollback journal.
+	if len(data) >= 20 && data[18] == 2 && data[19] == 2 {
+		data[18] = 1
+		data[19] = 1
+	}
+
+	sectors := divRoundUp(db.size, sectorSize)
+	db.data = make([]*[sectorSize]byte, sectors)
+	for i := range db.data {
+		sector := data[i*sectorSize:]
+		if len(sector) >= sectorSize {
+			db.data[i] = (*[sectorSize]byte)(sector)
+		} else {
+			db.data[i] = new([sectorSize]byte)
+			copy((*db.data[i])[:], sector)
+		}
+	}
+
+	memoryDBs[name] = db
+}
+
+// Delete deletes a shared memory database.
+func Delete(name string) {
+	memoryMtx.Lock()
+	defer memoryMtx.Unlock()
+	delete(memoryDBs, name)
+}