runtime environment consistency (mainly about fd 0-2)

[yamt]

it might make sense to provide a bit more consistent environment for tests.
eg. create a tty for fd 0-2

a few possible places where it can be done:

• someone who invokes our test runner (as of today)
• our test runner
• runtime adapter
• runtime itself

open questions:

• how much flexibility do we want? is it good enough to always assign fd 0-2 to a tty?
• do we want to support runtimes which don't "share" fd 0-2 with host fds?
• what to do for non-posix host?

cf.
yamt/toywasm@570e670
bytecodealliance/wasm-micro-runtime#2576