Fixes https://github.com/pulumi/pulumi/issues/12738https://github.com/pulumi/pulumi/pull/11834 turned on the prealloc
linter and changed a load of slice uses from just `var x T[]` to `x :=
make([]T, 0, preallocSize)`. This was good for performance but it turns
out there are a number of places in the codebase that treat a `nil`
slice as semnatically different to an empty slice.
Trying to test that, or even reason that through for every callsite is
untractable, so this PR replaces all expressions of the form `make([]T,
0, size)` with a call to `slice.Prealloc[T](size)`. When size is 0 that
returns a nil array, rather than an empty array.
Previously codegen would output hyphens into the names of symbols such
as functions, variable names, etc. This fix converts hyphens to
underscores, making them valid code in Go and Python.