Re-export more rustc_span::symbol things from rustc_span.

`rustc_span::symbol` defines some things that are re-exported from
`rustc_span`, such as `Symbol` and `sym`. But it doesn't re-export some
closely related things such as `Ident` and `kw`. So you can do `use
rustc_span::{Symbol, sym}` but you have to do `use
rustc_span::symbol::{Ident, kw}`, which is inconsistent for no good
reason.

This commit re-exports `Ident`, `kw`, and `MacroRulesNormalizedIdent`,
and changes many `rustc_span::symbol::` qualifiers in `compiler/` to
`rustc_span::`. This is a 200+ net line of code reduction, mostly
because many files with two `use rustc_span` items can be reduced to
one.

Author: nnethercote

src/intrinsics/mod.rs

@@ -23,7 +23,7 @@ use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::layout::ValidityRequirement;
 use rustc_middle::ty::print::{with_no_trimmed_paths, with_no_visible_paths};
 use rustc_span::source_map::Spanned;
-use rustc_span::symbol::{Symbol, sym};
+use rustc_span::{Symbol, sym};
 
 pub(crate) use self::llvm::codegen_llvm_intrinsic_call;
 use crate::cast::clif_intcast;

src/main_shim.rs

@@ -2,8 +2,7 @@ use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_hir::LangItem;
 use rustc_middle::ty::{AssocKind, GenericArg};
 use rustc_session::config::{EntryFnType, sigpipe};
-use rustc_span::DUMMY_SP;
-use rustc_span::symbol::Ident;
+use rustc_span::{DUMMY_SP, Ident};
 
 use crate::prelude::*;