[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_unix.go

@@ -0,0 +1,33 @@
+//go:build unix && !sqlite3_nosys
+
+package vfs
+
+import (
+	"os"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+)
+
+func osAccess(path string, flags AccessFlag) error {
+	var access uint32 // unix.F_OK
+	switch flags {
+	case ACCESS_READWRITE:
+		access = unix.R_OK | unix.W_OK
+	case ACCESS_READ:
+		access = unix.R_OK
+	}
+	return unix.Access(path, access)
+}
+
+func osSetMode(file *os.File, modeof string) error {
+	fi, err := os.Stat(modeof)
+	if err != nil {
+		return err
+	}
+	file.Chmod(fi.Mode())
+	if sys, ok := fi.Sys().(*syscall.Stat_t); ok {
+		file.Chown(int(sys.Uid), int(sys.Gid))
+	}
+	return nil
+}