[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/registry.go

@@ -0,0 +1,48 @@
+package vfs
+
+import "sync"
+
+var (
+	// +checklocks:vfsRegistryMtx
+	vfsRegistry    map[string]VFS
+	vfsRegistryMtx sync.RWMutex
+)
+
+// Find returns a VFS given its name.
+// If there is no match, nil is returned.
+// If name is empty, the default VFS is returned.
+//
+// https://sqlite.org/c3ref/vfs_find.html
+func Find(name string) VFS {
+	if name == "" || name == "os" {
+		return vfsOS{}
+	}
+	vfsRegistryMtx.RLock()
+	defer vfsRegistryMtx.RUnlock()
+	return vfsRegistry[name]
+}
+
+// Register registers a VFS.
+// Empty and "os" are reserved names.
+//
+// https://sqlite.org/c3ref/vfs_find.html
+func Register(name string, vfs VFS) {
+	if name == "" || name == "os" {
+		return
+	}
+	vfsRegistryMtx.Lock()
+	defer vfsRegistryMtx.Unlock()
+	if vfsRegistry == nil {
+		vfsRegistry = map[string]VFS{}
+	}
+	vfsRegistry[name] = vfs
+}
+
+// Unregister unregisters a VFS.
+//
+// https://sqlite.org/c3ref/vfs_find.html
+func Unregister(name string) {
+	vfsRegistryMtx.Lock()
+	defer vfsRegistryMtx.Unlock()
+	delete(vfsRegistry, name)
+}