Refactor away resolve_name_in_module in resolve_imports.rs

Rewrite and improve the core name resolution procedure in NameResolution::result and Module::resolve_name

Refactor the duplicate checking code into NameResolution::try_define

Refactor away the fields id and is_public of ImportResolution and rename ImportResolution to NameResolution

NameBinding now encodes these directly with binding.is_public() and (binding.is_public() && binding.is_import()) (respectively)

another and were not previously instrumented.

Refactor away NameBindings, NsDef, ImportResolutionPerNamespace, DuplicateCheckingMode, and NamespaceDefinition.

Resolve: Fix an ICE that occurs when an identifier refers to an indeterminate import (i.e. one that is not resolved and not known to have failed)

This fixes a bug in which items in a block are shadowed by local variables and type parameters that are in scope.
It is a [breaking-change]. For example, the following code breaks:

```rust
fn foo() {
    let mut f = 1;
    {
        fn f() {}
        f += 1; // This will now resolve to the function instead of the local variable
    }
}
```

Any breakage can be fixed by renaming the item that is no longer shadowed.

This commit removes the `-D warnings` flag being passed through the makefiles to
all crates to instead be a crate attribute. We want these attributes always
applied for all our standard builds, and this is more amenable to Cargo-based
builds as well.

Note that all `deny(warnings)` attributes are gated with a `cfg(stage0)`
attribute currently to match the same semantics we have today

resolve: use arena allocation instead of reference counting for `Module`s to fix memory leaks from Rc cycles