[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/readfs.go

@@ -0,0 +1,117 @@
+package sysfs
+
+import (
+	"io/fs"
+
+	experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+)
+
+type ReadFS struct {
+	experimentalsys.FS
+}
+
+// OpenFile implements the same method as documented on sys.FS
+func (r *ReadFS) OpenFile(path string, flag experimentalsys.Oflag, perm fs.FileMode) (experimentalsys.File, experimentalsys.Errno) {
+	// Mask the mutually exclusive bits as they determine write mode.
+	switch flag & (experimentalsys.O_RDONLY | experimentalsys.O_WRONLY | experimentalsys.O_RDWR) {
+	case experimentalsys.O_WRONLY, experimentalsys.O_RDWR:
+		// Return the correct error if a directory was opened for write.
+		if flag&experimentalsys.O_DIRECTORY != 0 {
+			return nil, experimentalsys.EISDIR
+		}
+		return nil, experimentalsys.ENOSYS
+	default: // sys.O_RDONLY (integer zero) so we are ok!
+	}
+
+	f, errno := r.FS.OpenFile(path, flag, perm)
+	if errno != 0 {
+		return nil, errno
+	}
+	return &readFile{f}, 0
+}
+
+// Mkdir implements the same method as documented on sys.FS
+func (r *ReadFS) Mkdir(path string, perm fs.FileMode) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Chmod implements the same method as documented on sys.FS
+func (r *ReadFS) Chmod(path string, perm fs.FileMode) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Rename implements the same method as documented on sys.FS
+func (r *ReadFS) Rename(from, to string) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Rmdir implements the same method as documented on sys.FS
+func (r *ReadFS) Rmdir(path string) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Link implements the same method as documented on sys.FS
+func (r *ReadFS) Link(_, _ string) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Symlink implements the same method as documented on sys.FS
+func (r *ReadFS) Symlink(_, _ string) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Unlink implements the same method as documented on sys.FS
+func (r *ReadFS) Unlink(path string) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// Utimens implements the same method as documented on sys.FS
+func (r *ReadFS) Utimens(path string, atim, mtim int64) experimentalsys.Errno {
+	return experimentalsys.EROFS
+}
+
+// compile-time check to ensure readFile implements api.File.
+var _ experimentalsys.File = (*readFile)(nil)
+
+type readFile struct {
+	experimentalsys.File
+}
+
+// Write implements the same method as documented on sys.File.
+func (r *readFile) Write([]byte) (int, experimentalsys.Errno) {
+	return 0, r.writeErr()
+}
+
+// Pwrite implements the same method as documented on sys.File.
+func (r *readFile) Pwrite([]byte, int64) (n int, errno experimentalsys.Errno) {
+	return 0, r.writeErr()
+}
+
+// Truncate implements the same method as documented on sys.File.
+func (r *readFile) Truncate(int64) experimentalsys.Errno {
+	return r.writeErr()
+}
+
+// Sync implements the same method as documented on sys.File.
+func (r *readFile) Sync() experimentalsys.Errno {
+	return experimentalsys.EBADF
+}
+
+// Datasync implements the same method as documented on sys.File.
+func (r *readFile) Datasync() experimentalsys.Errno {
+	return experimentalsys.EBADF
+}
+
+// Utimens implements the same method as documented on sys.File.
+func (r *readFile) Utimens(int64, int64) experimentalsys.Errno {
+	return experimentalsys.EBADF
+}
+
+func (r *readFile) writeErr() experimentalsys.Errno {
+	if isDir, errno := r.IsDir(); errno != 0 {
+		return errno
+	} else if isDir {
+		return experimentalsys.EISDIR
+	}
+	return experimentalsys.EBADF
+}