[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/internal/util/mem.go

@@ -0,0 +1,134 @@
+package util
+
+import (
+	"bytes"
+	"math"
+
+	"github.com/tetratelabs/wazero/api"
+)
+
+func View(mod api.Module, ptr uint32, size uint64) []byte {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	if size > math.MaxUint32 {
+		panic(RangeErr)
+	}
+	if size == 0 {
+		return nil
+	}
+	buf, ok := mod.Memory().Read(ptr, uint32(size))
+	if !ok {
+		panic(RangeErr)
+	}
+	return buf
+}
+
+func ReadUint8(mod api.Module, ptr uint32) uint8 {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	v, ok := mod.Memory().ReadByte(ptr)
+	if !ok {
+		panic(RangeErr)
+	}
+	return v
+}
+
+func ReadUint32(mod api.Module, ptr uint32) uint32 {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	v, ok := mod.Memory().ReadUint32Le(ptr)
+	if !ok {
+		panic(RangeErr)
+	}
+	return v
+}
+
+func WriteUint8(mod api.Module, ptr uint32, v uint8) {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	ok := mod.Memory().WriteByte(ptr, v)
+	if !ok {
+		panic(RangeErr)
+	}
+}
+
+func WriteUint32(mod api.Module, ptr uint32, v uint32) {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	ok := mod.Memory().WriteUint32Le(ptr, v)
+	if !ok {
+		panic(RangeErr)
+	}
+}
+
+func ReadUint64(mod api.Module, ptr uint32) uint64 {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	v, ok := mod.Memory().ReadUint64Le(ptr)
+	if !ok {
+		panic(RangeErr)
+	}
+	return v
+}
+
+func WriteUint64(mod api.Module, ptr uint32, v uint64) {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	ok := mod.Memory().WriteUint64Le(ptr, v)
+	if !ok {
+		panic(RangeErr)
+	}
+}
+
+func ReadFloat64(mod api.Module, ptr uint32) float64 {
+	return math.Float64frombits(ReadUint64(mod, ptr))
+}
+
+func WriteFloat64(mod api.Module, ptr uint32, v float64) {
+	WriteUint64(mod, ptr, math.Float64bits(v))
+}
+
+func ReadString(mod api.Module, ptr, maxlen uint32) string {
+	if ptr == 0 {
+		panic(NilErr)
+	}
+	switch maxlen {
+	case 0:
+		return ""
+	case math.MaxUint32:
+		// avoid overflow
+	default:
+		maxlen = maxlen + 1
+	}
+	mem := mod.Memory()
+	buf, ok := mem.Read(ptr, maxlen)
+	if !ok {
+		buf, ok = mem.Read(ptr, mem.Size()-ptr)
+		if !ok {
+			panic(RangeErr)
+		}
+	}
+	if i := bytes.IndexByte(buf, 0); i < 0 {
+		panic(NoNulErr)
+	} else {
+		return string(buf[:i])
+	}
+}
+
+func WriteBytes(mod api.Module, ptr uint32, b []byte) {
+	buf := View(mod, ptr, uint64(len(b)))
+	copy(buf, b)
+}
+
+func WriteString(mod api.Module, ptr uint32, s string) {
+	buf := View(mod, ptr, uint64(len(s)+1))
+	buf[len(s)] = 0
+	copy(buf, s)
+}