feat(hir): expose hir from parsing context

[grandizzy]

• access Hir from calling ParsingContext::parse_and_lower_to_hir

[DaniPopes]

should maintain style of the other fns, using hir:: as a module instead of importing

[grandizzy]

changed in 9c654cc

[DaniPopes]

I want to avoid any code dup here and also avoid using Hir directly, but instead through gcx; I think what we can do here is something like this

fn parse_and_resolve() {
    let gcx = *parse_and_lower()?;
    analysis(gcx)?;
    Ok(())
}

fn parse_and_lower<'hir>(pcx: '_, hir_arena: 'hir) -> impl Deref<Target=Gcx<'hir>> {
    // all the code currently in parse_and_resolve ...
    GcxWrapper(...)
}

struct GcxWrapper(GlobalContext);
impl Deref for GcxWrapper {
    // move the unsafe here
}
impl Drop for GcxWrapper {
    // move from OnDrop closure
}

This way we can keep the drop impl and avoid a closure for using Gcx

[grandizzy]

@DaniPopes would the approach in 9c654cc which doesn't introduce a new wrapper work?