This syscall doesn't need allocating stack or TLS and it's expected from the application
to do that instead. E.g. WASI-libc already does this for `pthread_create`.
Also fix some of the examples to allocate memory for stack and not use stack before
the stack pointer is set to a correct value.
For now this implementation uses thread manager.
Not sure whether thread manager is needed in that case. In the future there'll be likely another syscall added (for pthread_exit) and for that we might need some kind of thread management - with that in mind, we keep thread manager for now and will refactor this later if needed.
