[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/internal/engine/wazevo/hostmodule.go

@@ -0,0 +1,82 @@
+package wazevo
+
+import (
+	"encoding/binary"
+	"reflect"
+	"unsafe"
+
+	"github.com/tetratelabs/wazero/experimental"
+	"github.com/tetratelabs/wazero/internal/wasm"
+)
+
+func buildHostModuleOpaque(m *wasm.Module, listeners []experimental.FunctionListener) moduleContextOpaque {
+	size := len(m.CodeSection)*16 + 32
+	ret := newAlignedOpaque(size)
+
+	binary.LittleEndian.PutUint64(ret[0:], uint64(uintptr(unsafe.Pointer(m))))
+
+	if len(listeners) > 0 {
+		sliceHeader := (*reflect.SliceHeader)(unsafe.Pointer(&listeners))
+		binary.LittleEndian.PutUint64(ret[8:], uint64(sliceHeader.Data))
+		binary.LittleEndian.PutUint64(ret[16:], uint64(sliceHeader.Len))
+		binary.LittleEndian.PutUint64(ret[24:], uint64(sliceHeader.Cap))
+	}
+
+	offset := 32
+	for i := range m.CodeSection {
+		goFn := m.CodeSection[i].GoFunc
+		writeIface(goFn, ret[offset:])
+		offset += 16
+	}
+	return ret
+}
+
+func hostModuleFromOpaque(opaqueBegin uintptr) *wasm.Module {
+	var opaqueViewOverSlice []byte
+	sh := (*reflect.SliceHeader)(unsafe.Pointer(&opaqueViewOverSlice))
+	sh.Data = opaqueBegin
+	sh.Len = 32
+	sh.Cap = 32
+	return *(**wasm.Module)(unsafe.Pointer(&opaqueViewOverSlice[0]))
+}
+
+func hostModuleListenersSliceFromOpaque(opaqueBegin uintptr) []experimental.FunctionListener {
+	var opaqueViewOverSlice []byte
+	sh := (*reflect.SliceHeader)(unsafe.Pointer(&opaqueViewOverSlice))
+	sh.Data = opaqueBegin
+	sh.Len = 32
+	sh.Cap = 32
+
+	b := binary.LittleEndian.Uint64(opaqueViewOverSlice[8:])
+	l := binary.LittleEndian.Uint64(opaqueViewOverSlice[16:])
+	c := binary.LittleEndian.Uint64(opaqueViewOverSlice[24:])
+	var ret []experimental.FunctionListener
+	sh = (*reflect.SliceHeader)(unsafe.Pointer(&ret))
+	sh.Data = uintptr(b)
+	setSliceLimits(sh, uintptr(l), uintptr(c))
+	return ret
+}
+
+func hostModuleGoFuncFromOpaque[T any](index int, opaqueBegin uintptr) T {
+	offset := uintptr(index*16) + 32
+	ptr := opaqueBegin + offset
+
+	var opaqueViewOverFunction []byte
+	sh := (*reflect.SliceHeader)(unsafe.Pointer(&opaqueViewOverFunction))
+	sh.Data = ptr
+	sh.Len = 16
+	sh.Cap = 16
+	return readIface(opaqueViewOverFunction).(T)
+}
+
+func writeIface(goFn interface{}, buf []byte) {
+	goFnIface := *(*[2]uint64)(unsafe.Pointer(&goFn))
+	binary.LittleEndian.PutUint64(buf, goFnIface[0])
+	binary.LittleEndian.PutUint64(buf[8:], goFnIface[1])
+}
+
+func readIface(buf []byte) interface{} {
+	b := binary.LittleEndian.Uint64(buf)
+	s := binary.LittleEndian.Uint64(buf[8:])
+	return *(*interface{})(unsafe.Pointer(&[2]uint64{b, s}))
+}