Resolve aliases before inserting values into the live set

[fitzgen]

This fixes a fuzz bug found in the development of #8941

[bjorn3]

Why does the alias resolving need to be done? cranelift-frontend can and does change aliases on the fly. It feels iffy to immediately resolve them inside cranelift-frontend as there is nothing preventing the alias that was resolved to be changed later.

[fitzgen]

Why does the alias resolving need to be done?

Because otherwise we would need to have a reverse-aliases map from a value to all of the values that alias it. This is necessary because when we find a definition, we kill it from the live set, so at that point we only have the non-alias value.

It feels iffy to immediately resolve them inside cranelift-frontend as there is nothing preventing the alias that was resolved to be changed later.

Note that the safepoint spilling and its liveness analysis happens as part of finishing a FunctionBuilder, so we don't need to worry about anything changing under our feet here.