WebAssembly
Fuzzer: Adjust feature fuzzing frequency
We used to fuzz MVP 1/3, all 1/3, and a mixture 1/3, but that gives far too much priority to the MVP which is increasingly less important. It is also a good idea to give "all" more priority as that enables more initial content to run (the fuzzer will discard initial content if it doesn't validate with the features chosen in the current iteration).
Actually I may need to change the probabilities here, since I forgot that enabling all features disables parts of the fuzzer... for example enabling simd disables running d8 (since v128 on the boundary traps - we can't compare those values). I'll think about some solution to that first maybe.
After recent PRs landing, enabling all features no longer limits V8 fuzzing. It does still limit some things like wasm2js fuzzing, but that is low priority, and so this can land.