[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/sysfs/dirfs.go

@@ -0,0 +1,99 @@
+package sysfs
+
+import (
+	"io/fs"
+	"os"
+
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+	"github.com/tetratelabs/wazero/internal/platform"
+	"github.com/tetratelabs/wazero/sys"
+)
+
+func DirFS(dir string) experimentalsys.FS {
+	return &dirFS{
+		dir:        dir,
+		cleanedDir: ensureTrailingPathSeparator(dir),
+	}
+}
+
+func ensureTrailingPathSeparator(dir string) string {
+	if !os.IsPathSeparator(dir[len(dir)-1]) {
+		return dir + string(os.PathSeparator)
+	}
+	return dir
+}
+
+// dirFS is not exported because the input fields must be maintained together.
+// This is likely why os.DirFS doesn't, either!
+type dirFS struct {
+	experimentalsys.UnimplementedFS
+
+	dir string
+	// cleanedDir is for easier OS-specific concatenation, as it always has
+	// a trailing path separator.
+	cleanedDir string
+}
+
+// String implements fmt.Stringer
+func (d *dirFS) String() string {
+	return d.dir
+}
+
+// OpenFile implements the same method as documented on sys.FS
+func (d *dirFS) OpenFile(path string, flag experimentalsys.Oflag, perm fs.FileMode) (experimentalsys.File, experimentalsys.Errno) {
+	return OpenOSFile(d.join(path), flag, perm)
+}
+
+// Lstat implements the same method as documented on sys.FS
+func (d *dirFS) Lstat(path string) (sys.Stat_t, experimentalsys.Errno) {
+	return lstat(d.join(path))
+}
+
+// Stat implements the same method as documented on sys.FS
+func (d *dirFS) Stat(path string) (sys.Stat_t, experimentalsys.Errno) {
+	return stat(d.join(path))
+}
+
+// Mkdir implements the same method as documented on sys.FS
+func (d *dirFS) Mkdir(path string, perm fs.FileMode) (errno experimentalsys.Errno) {
+	err := os.Mkdir(d.join(path), perm)
+	if errno = experimentalsys.UnwrapOSError(err); errno == experimentalsys.ENOTDIR {
+		errno = experimentalsys.ENOENT
+	}
+	return
+}
+
+// Readlink implements the same method as documented on sys.FS
+func (d *dirFS) Readlink(path string) (string, experimentalsys.Errno) {
+	// Note: do not use syscall.Readlink as that causes race on Windows.
+	// In any case, syscall.Readlink does almost the same logic as os.Readlink.
+	dst, err := os.Readlink(d.join(path))
+	if err != nil {
+		return "", experimentalsys.UnwrapOSError(err)
+	}
+	return platform.ToPosixPath(dst), 0
+}
+
+// Rmdir implements the same method as documented on sys.FS
+func (d *dirFS) Rmdir(path string) experimentalsys.Errno {
+	return rmdir(d.join(path))
+}
+
+// Utimens implements the same method as documented on sys.FS
+func (d *dirFS) Utimens(path string, atim, mtim int64) experimentalsys.Errno {
+	return utimens(d.join(path), atim, mtim)
+}
+
+func (d *dirFS) join(path string) string {
+	switch path {
+	case "", ".", "/":
+		if d.cleanedDir == "/" {
+			return "/"
+		}
+		// cleanedDir includes an unnecessary delimiter for the root path.
+		return d.cleanedDir[:len(d.cleanedDir)-1]
+	}
+	// TODO: Enforce similar to safefilepath.FromFS(path), but be careful as
+	// relative path inputs are allowed. e.g. dir or path == ../
+	return d.cleanedDir + path
+}