Update CodeGen to enable the Luau::CodeGen::CodeGen_ColdFunctions flag, and set up random number generators for NCG.

[aatxe]

We got a bug report about IR and assembly generation failing sometimes. The circumstances for when this happen seem to be when the top-level function gets marked cold. We have a flag that we use in the luau CLI to avoid this issue, and we can set up the same flag to avoid the issue here. There's actually a secondary issue where, at the least, arm64 generation relies on offsetof extensively and we're currently building for wasm32, causing the offset math to not line up and the codegen to error out.

An example program demonstrating this bug:

local e: string = "lol"
local r = e:rep(3)
local x = string.rep(e, 3)
print(x)
print(r)
print(e)
local xd = buffer.create(32)
buffer.writeu32(xd, 29, 0)

It's a bit funny to learn that NCG relies on the host platform being 64-bit, but it's a non-trivial problem to work around. The easiest solution would be to enable wasm64, where the offsets will once again match up with our native architectures. Unfortunately, wasm64 is not supported in Safari as of the time of writing, and a significant portion of our Playground users are on Safari. An alternative solution would be to, from a host build, generate the entire table of offsets necessary, and then load that for the wasm build, rather than using offsetof directly. I'll look into the viability of this going forward, or if wasm64 support is on the horizon for Safari.