[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/sys/stdio.go

@@ -0,0 +1,128 @@
+package sys
+
+import (
+	"io"
+	"os"
+
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+	"github.com/tetratelabs/wazero/internal/fsapi"
+	"github.com/tetratelabs/wazero/internal/sysfs"
+	"github.com/tetratelabs/wazero/sys"
+)
+
+// StdinFile is a fs.ModeDevice file for use implementing FdStdin.
+// This is safer than reading from os.DevNull as it can never overrun
+// operating system file descriptors.
+type StdinFile struct {
+	noopStdinFile
+	io.Reader
+}
+
+// Read implements the same method as documented on sys.File
+func (f *StdinFile) Read(buf []byte) (int, experimentalsys.Errno) {
+	n, err := f.Reader.Read(buf)
+	return n, experimentalsys.UnwrapOSError(err)
+}
+
+type writerFile struct {
+	noopStdoutFile
+
+	w io.Writer
+}
+
+// Write implements the same method as documented on sys.File
+func (f *writerFile) Write(buf []byte) (int, experimentalsys.Errno) {
+	n, err := f.w.Write(buf)
+	return n, experimentalsys.UnwrapOSError(err)
+}
+
+// noopStdinFile is a fs.ModeDevice file for use implementing FdStdin. This is
+// safer than reading from os.DevNull as it can never overrun operating system
+// file descriptors.
+type noopStdinFile struct {
+	noopStdioFile
+}
+
+// Read implements the same method as documented on sys.File
+func (noopStdinFile) Read([]byte) (int, experimentalsys.Errno) {
+	return 0, 0 // Always EOF
+}
+
+// Poll implements the same method as documented on fsapi.File
+func (noopStdinFile) Poll(flag fsapi.Pflag, timeoutMillis int32) (ready bool, errno experimentalsys.Errno) {
+	if flag != fsapi.POLLIN {
+		return false, experimentalsys.ENOTSUP
+	}
+	return true, 0 // always ready to read nothing
+}
+
+// noopStdoutFile is a fs.ModeDevice file for use implementing FdStdout and
+// FdStderr.
+type noopStdoutFile struct {
+	noopStdioFile
+}
+
+// Write implements the same method as documented on sys.File
+func (noopStdoutFile) Write(buf []byte) (int, experimentalsys.Errno) {
+	return len(buf), 0 // same as io.Discard
+}
+
+type noopStdioFile struct {
+	experimentalsys.UnimplementedFile
+}
+
+// Stat implements the same method as documented on sys.File
+func (noopStdioFile) Stat() (sys.Stat_t, experimentalsys.Errno) {
+	return sys.Stat_t{Mode: modeDevice, Nlink: 1}, 0
+}
+
+// IsDir implements the same method as documented on sys.File
+func (noopStdioFile) IsDir() (bool, experimentalsys.Errno) {
+	return false, 0
+}
+
+// Close implements the same method as documented on sys.File
+func (noopStdioFile) Close() (errno experimentalsys.Errno) { return }
+
+// IsNonblock implements the same method as documented on fsapi.File
+func (noopStdioFile) IsNonblock() bool {
+	return false
+}
+
+// SetNonblock implements the same method as documented on fsapi.File
+func (noopStdioFile) SetNonblock(bool) experimentalsys.Errno {
+	return experimentalsys.ENOSYS
+}
+
+// Poll implements the same method as documented on fsapi.File
+func (noopStdioFile) Poll(fsapi.Pflag, int32) (ready bool, errno experimentalsys.Errno) {
+	return false, experimentalsys.ENOSYS
+}
+
+func stdinFileEntry(r io.Reader) (*FileEntry, error) {
+	if r == nil {
+		return &FileEntry{Name: "stdin", IsPreopen: true, File: &noopStdinFile{}}, nil
+	} else if f, ok := r.(*os.File); ok {
+		if f, err := sysfs.NewStdioFile(true, f); err != nil {
+			return nil, err
+		} else {
+			return &FileEntry{Name: "stdin", IsPreopen: true, File: f}, nil
+		}
+	} else {
+		return &FileEntry{Name: "stdin", IsPreopen: true, File: &StdinFile{Reader: r}}, nil
+	}
+}
+
+func stdioWriterFileEntry(name string, w io.Writer) (*FileEntry, error) {
+	if w == nil {
+		return &FileEntry{Name: name, IsPreopen: true, File: &noopStdoutFile{}}, nil
+	} else if f, ok := w.(*os.File); ok {
+		if f, err := sysfs.NewStdioFile(false, f); err != nil {
+			return nil, err
+		} else {
+			return &FileEntry{Name: name, IsPreopen: true, File: f}, nil
+		}
+	} else {
+		return &FileEntry{Name: name, IsPreopen: true, File: &writerFile{w: w}}, nil
+	}
+}