[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/vfs/os_darwin.go

@@ -0,0 +1,95 @@
+//go:build !(sqlite3_flock || sqlite3_nosys)
+
+package vfs
+
+import (
+	"io"
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	// https://github.com/apple/darwin-xnu/blob/main/bsd/sys/fcntl.h
+	_F_OFD_SETLK         = 90
+	_F_OFD_SETLKW        = 91
+	_F_OFD_SETLKWTIMEOUT = 93
+)
+
+type flocktimeout_t struct {
+	fl      unix.Flock_t
+	timeout unix.Timespec
+}
+
+func osSync(file *os.File, fullsync, _ /*dataonly*/ bool) error {
+	if fullsync {
+		return file.Sync()
+	}
+	return unix.Fsync(int(file.Fd()))
+}
+
+func osAllocate(file *os.File, size int64) error {
+	off, err := file.Seek(0, io.SeekEnd)
+	if err != nil {
+		return err
+	}
+	if size <= off {
+		return nil
+	}
+
+	store := unix.Fstore_t{
+		Flags:   unix.F_ALLOCATEALL | unix.F_ALLOCATECONTIG,
+		Posmode: unix.F_PEOFPOSMODE,
+		Offset:  0,
+		Length:  size - off,
+	}
+
+	// Try to get a continuous chunk of disk space.
+	err = unix.FcntlFstore(file.Fd(), unix.F_PREALLOCATE, &store)
+	if err != nil {
+		// OK, perhaps we are too fragmented, allocate non-continuous.
+		store.Flags = unix.F_ALLOCATEALL
+		unix.FcntlFstore(file.Fd(), unix.F_PREALLOCATE, &store)
+	}
+	return file.Truncate(size)
+}
+
+func osUnlock(file *os.File, start, len int64) _ErrorCode {
+	err := unix.FcntlFlock(file.Fd(), _F_OFD_SETLK, &unix.Flock_t{
+		Type:  unix.F_UNLCK,
+		Start: start,
+		Len:   len,
+	})
+	if err != nil {
+		return _IOERR_UNLOCK
+	}
+	return _OK
+}
+
+func osLock(file *os.File, typ int16, start, len int64, timeout time.Duration, def _ErrorCode) _ErrorCode {
+	lock := flocktimeout_t{fl: unix.Flock_t{
+		Type:  typ,
+		Start: start,
+		Len:   len,
+	}}
+	var err error
+	switch {
+	case timeout == 0:
+		err = unix.FcntlFlock(file.Fd(), _F_OFD_SETLK, &lock.fl)
+	case timeout < 0:
+		err = unix.FcntlFlock(file.Fd(), _F_OFD_SETLKW, &lock.fl)
+	default:
+		lock.timeout = unix.NsecToTimespec(int64(timeout / time.Nanosecond))
+		err = unix.FcntlFlock(file.Fd(), _F_OFD_SETLKWTIMEOUT, &lock.fl)
+	}
+	return osLockErrorCode(err, def)
+}
+
+func osReadLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCode {
+	return osLock(file, unix.F_RDLCK, start, len, timeout, _IOERR_RDLOCK)
+}
+
+func osWriteLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCode {
+	return osLock(file, unix.F_WRLCK, start, len, timeout, _IOERR_LOCK)
+}