[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/memory.go

@@ -0,0 +1,50 @@
+package experimental
+
+import (
+	"context"
+
+	"github.com/tetratelabs/wazero/internal/expctxkeys"
+)
+
+// MemoryAllocator is a memory allocation hook,
+// invoked to create a LinearMemory.
+type MemoryAllocator interface {
+	// Allocate should create a new LinearMemory with the given specification:
+	// cap is the suggested initial capacity for the backing []byte,
+	// and max the maximum length that will ever be requested.
+	//
+	// Notes:
+	//   - To back a shared memory, the address of the backing []byte cannot
+	//     change. This is checked at runtime. Implementations should document
+	//     if the returned LinearMemory meets this requirement.
+	Allocate(cap, max uint64) LinearMemory
+}
+
+// MemoryAllocatorFunc is a convenience for defining inlining a MemoryAllocator.
+type MemoryAllocatorFunc func(cap, max uint64) LinearMemory
+
+// Allocate implements MemoryAllocator.Allocate.
+func (f MemoryAllocatorFunc) Allocate(cap, max uint64) LinearMemory {
+	return f(cap, max)
+}
+
+// LinearMemory is an expandable []byte that backs a Wasm linear memory.
+type LinearMemory interface {
+	// Reallocates the linear memory to size bytes in length.
+	//
+	// Notes:
+	//   - To back a shared memory, Reallocate can't change the address of the
+	//     backing []byte (only its length/capacity may change).
+	Reallocate(size uint64) []byte
+	// Free the backing memory buffer.
+	Free()
+}
+
+// WithMemoryAllocator registers the given MemoryAllocator into the given
+// context.Context.
+func WithMemoryAllocator(ctx context.Context, allocator MemoryAllocator) context.Context {
+	if allocator != nil {
+		return context.WithValue(ctx, expctxkeys.MemoryAllocatorKey{}, allocator)
+	}
+	return ctx
+}