Function optimizations

[vouillon]

Combination of many optimizations. I'm going to split this into several PRs.

• Do not store the code pointer in closures if we know we don't need it (Closure optimization: omit code pointer when not used #2059)
• Unboxing of floats and integers within a function (Number unboxing #2069)
• Function parameters: pass integers as i32 rather than (ref eq) when possible
• Function parameters: unbox floats and integers
• Unbox return values
• Reference unboxing (Reference unboxing #1958)
• Specialization of number comparisons (Wasm: specialization of number comparisons and bigarray operations #1954)
• Specialization of bigarray operations (Wasm: specialization of number comparisons and bigarray operations #1954)