Add an insecure interface.

[sunfishcode]

Add an insecure interface, and split the seed function into its own interface, producing three interfaces:

• random, for secure pseudo-random numbers
• insecure, for pseudo-random numbers that are not secure
• insecure-seed, for supporting hash-map DoS protection

We've gone back and forth on whether such an API is desirable, but it's now motivated by the need to implement things like JavaScript's Math.random, which want to be random, don't want to run their own PRNG, and don't need to be secure. And in fact, they specifically don't want to be secure, because they want to allow hosts to make them deterministic if they wish to.

[pannous]

maybe random should return true random numbers and pseudo-random should return pseudo-random numbers

[sunfishcode]

True Random Number Generators (TRNG) are specialized things which are complex to use effectively, complex to implement, and very few applications need to use them (directly). Such things could be added to WASI, but I myself am not proposing to do so at this time.

If WASI does add TRNG APIs, I imagine we'll want to give them qualified names, rather than just calling them "random", to help avoid people using them without realizing what they're getting themselves into.