[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_linux.go

@@ -0,0 +1,71 @@
+//go:build !(sqlite3_flock || sqlite3_nosys)
+
+package vfs
+
+import (
+	"math/rand"
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+func osSync(file *os.File, _ /*fullsync*/, _ /*dataonly*/ bool) error {
+	// SQLite trusts Linux's fdatasync for all fsync's.
+	return unix.Fdatasync(int(file.Fd()))
+}
+
+func osAllocate(file *os.File, size int64) error {
+	if size == 0 {
+		return nil
+	}
+	return unix.Fallocate(int(file.Fd()), 0, 0, size)
+}
+
+func osUnlock(file *os.File, start, len int64) _ErrorCode {
+	err := unix.FcntlFlock(file.Fd(), unix.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 := unix.Flock_t{
+		Type:  typ,
+		Start: start,
+		Len:   len,
+	}
+	var err error
+	switch {
+	case timeout == 0:
+		err = unix.FcntlFlock(file.Fd(), unix.F_OFD_SETLK, &lock)
+	case timeout < 0:
+		err = unix.FcntlFlock(file.Fd(), unix.F_OFD_SETLKW, &lock)
+	default:
+		before := time.Now()
+		for {
+			err = unix.FcntlFlock(file.Fd(), unix.F_OFD_SETLK, &lock)
+			if errno, _ := err.(unix.Errno); errno != unix.EAGAIN {
+				break
+			}
+			if timeout < time.Since(before) {
+				break
+			}
+			osSleep(time.Duration(rand.Int63n(int64(time.Millisecond))))
+		}
+	}
+	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)
+}