[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/fsapi/file.go

@@ -0,0 +1,69 @@
+package fsapi
+
+import experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+
+// File includes methods not yet ready to document for end users, notably
+// non-blocking functionality.
+//
+// Particularly, Poll is subject to debate. For example, whether a user should
+// be able to choose how to implement timeout or not. Currently, this interface
+// allows the user to choose to sleep or use native polling, and which choice
+// they make impacts thread behavior as summarized here:
+// https://github.com/tetratelabs/wazero/pull/1606#issuecomment-1665475516
+type File interface {
+	experimentalsys.File
+
+	// IsNonblock returns true if the file was opened with O_NONBLOCK, or
+	// SetNonblock was successfully enabled on this file.
+	//
+	// # Notes
+	//
+	//   - This might not match the underlying state of the file descriptor if
+	//     the file was not opened via OpenFile.
+	IsNonblock() bool
+
+	// SetNonblock toggles the non-blocking mode (O_NONBLOCK) of this file.
+	//
+	// # Errors
+	//
+	// A zero Errno is success. The below are expected otherwise:
+	//   - ENOSYS: the implementation does not support this function.
+	//   - EBADF: the file or directory was closed.
+	//
+	// # Notes
+	//
+	//   - This is like syscall.SetNonblock and `fcntl` with O_NONBLOCK in
+	//     POSIX. See https://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html
+	SetNonblock(enable bool) experimentalsys.Errno
+
+	// Poll returns if the file has data ready to be read or written.
+	//
+	// # Parameters
+	//
+	// The `flag` parameter determines which event to await, such as POLLIN,
+	// POLLOUT, or a combination like `POLLIN|POLLOUT`.
+	//
+	// The `timeoutMillis` parameter is how long to block for an event, or
+	// interrupted, in milliseconds. There are two special values:
+	//   - zero returns immediately
+	//   - any negative value blocks any amount of time
+	//
+	// # Results
+	//
+	// `ready` means there was data ready to read or written. False can mean no
+	// event was ready or `errno` is not zero.
+	//
+	// A zero `errno` is success. The below are expected otherwise:
+	//   - ENOSYS: the implementation does not support this function.
+	//   - ENOTSUP: the implementation does not the flag combination.
+	//   - EINTR: the call was interrupted prior to an event.
+	//
+	// # Notes
+	//
+	//   - This is like `poll` in POSIX, for a single file.
+	//     See https://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html
+	//   - No-op files, such as those which read from /dev/null, should return
+	//     immediately true, as data will never become available.
+	//   - See /RATIONALE.md for detailed notes including impact of blocking.
+	Poll(flag Pflag, timeoutMillis int32) (ready bool, errno experimentalsys.Errno)
+}

vendor/github.com/tetratelabs/wazero/internal/fsapi/poll.go

@@ -0,0 +1,20 @@
+package fsapi
+
+// Pflag are bit flags used for File.Poll. Values, including zero, should not
+// be interpreted numerically. Instead, use by constants prefixed with 'POLL'.
+//
+// # Notes
+//
+//   - This is like `pollfd.events` flags for `poll` in POSIX. See
+//     https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/poll.h.html
+type Pflag uint32
+
+// Only define bitflags we support and are needed by `poll_oneoff` in wasip1
+// See https://github.com/WebAssembly/WASI/blob/snapshot-01/phases/snapshot/docs.md#eventrwflags
+const (
+	// POLLIN is a read event.
+	POLLIN Pflag = 1 << iota
+
+	// POLLOUT is a write event.
+	POLLOUT
+)

vendor/github.com/tetratelabs/wazero/internal/fsapi/unimplemented.go

@@ -0,0 +1,27 @@
+package fsapi
+
+import experimentalsys "github.com/tetratelabs/wazero/experimental/sys"
+
+func Adapt(f experimentalsys.File) File {
+	if f, ok := f.(File); ok {
+		return f
+	}
+	return unimplementedFile{f}
+}
+
+type unimplementedFile struct{ experimentalsys.File }
+
+// IsNonblock implements File.IsNonblock
+func (unimplementedFile) IsNonblock() bool {
+	return false
+}
+
+// SetNonblock implements File.SetNonblock
+func (unimplementedFile) SetNonblock(bool) experimentalsys.Errno {
+	return experimentalsys.ENOSYS
+}
+
+// Poll implements File.Poll
+func (unimplementedFile) Poll(Pflag, int32) (ready bool, errno experimentalsys.Errno) {
+	return false, experimentalsys.ENOSYS
+}