[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/tetratelabs/wazero/experimental/checkpoint.go

@@ -0,0 +1,48 @@
+package experimental
+
+import (
+	"context"
+
+	"github.com/tetratelabs/wazero/internal/expctxkeys"
+)
+
+// Snapshot holds the execution state at the time of a Snapshotter.Snapshot call.
+type Snapshot interface {
+	// Restore sets the Wasm execution state to the capture. Because a host function
+	// calling this is resetting the pointer to the executation stack, the host function
+	// will not be able to return values in the normal way. ret is a slice of values the
+	// host function intends to return from the restored function.
+	Restore(ret []uint64)
+}
+
+// Snapshotter allows host functions to snapshot the WebAssembly execution environment.
+type Snapshotter interface {
+	// Snapshot captures the current execution state.
+	Snapshot() Snapshot
+}
+
+// EnableSnapshotterKey is a context key to indicate that snapshotting should be enabled.
+// The context.Context passed to a exported function invocation should have this key set
+// to a non-nil value, and host functions will be able to retrieve it using SnapshotterKey.
+//
+// Deprecated: use WithSnapshotter to enable snapshots.
+type EnableSnapshotterKey = expctxkeys.EnableSnapshotterKey
+
+// WithSnapshotter enables snapshots.
+// Passing the returned context to a exported function invocation enables snapshots,
+// and allows host functions to retrieve the Snapshotter using GetSnapshotter.
+func WithSnapshotter(ctx context.Context) context.Context {
+	return context.WithValue(ctx, expctxkeys.EnableSnapshotterKey{}, struct{}{})
+}
+
+// SnapshotterKey is a context key to access a Snapshotter from a host function.
+// It is only present if EnableSnapshotter was set in the function invocation context.
+//
+// Deprecated: use GetSnapshotter to get the snapshotter.
+type SnapshotterKey = expctxkeys.SnapshotterKey
+
+// GetSnapshotter gets the Snapshotter from a host function.
+// It is only present if WithSnapshotter was called with the function invocation context.
+func GetSnapshotter(ctx context.Context) Snapshotter {
+	return ctx.Value(expctxkeys.SnapshotterKey{}).(Snapshotter)
+}