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.

compiler/rustc_mir_transform/src/coroutine.rs

@@ -73,9 +73,8 @@ use rustc_mir_dataflow::impls::{
     always_storage_live_locals,
 };
 use rustc_mir_dataflow::{Analysis, Results, ResultsVisitor};
-use rustc_span::Span;
 use rustc_span::def_id::{DefId, LocalDefId};
-use rustc_span::symbol::sym;
+use rustc_span::{Span, sym};
 use rustc_target::spec::PanicStrategy;
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::infer::TyCtxtInferExt as _;

compiler/rustc_mir_transform/src/coroutine/by_move_body.rs

@@ -78,7 +78,7 @@ use rustc_middle::hir::place::{Projection, ProjectionKind};
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::{self, dump_mir};
 use rustc_middle::ty::{self, InstanceKind, Ty, TyCtxt, TypeVisitableExt};
-use rustc_span::symbol::kw;
+use rustc_span::kw;
 
 pub(crate) fn coroutine_by_move_body_def_id<'tcx>(
     tcx: TyCtxt<'tcx>,

compiler/rustc_mir_transform/src/function_item_references.rs

@@ -5,9 +5,8 @@ use rustc_middle::mir::visit::Visitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, EarlyBinder, GenericArgsRef, Ty, TyCtxt};
 use rustc_session::lint::builtin::FUNCTION_ITEM_REFERENCES;
-use rustc_span::Span;
 use rustc_span::source_map::Spanned;
-use rustc_span::symbol::sym;
+use rustc_span::{Span, sym};
 
 use crate::errors;
 

compiler/rustc_mir_transform/src/instsimplify.rs

@@ -7,8 +7,7 @@ use rustc_middle::bug;
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::ValidityRequirement;
 use rustc_middle::ty::{self, GenericArgsRef, Ty, TyCtxt, layout};
-use rustc_span::symbol::Symbol;
-use rustc_span::{DUMMY_SP, sym};
+use rustc_span::{DUMMY_SP, Symbol, sym};
 
 use crate::simplify::simplify_duplicate_switch_targets;
 use crate::take_array;

compiler/rustc_mir_transform/src/lower_intrinsics.rs

@@ -3,7 +3,7 @@
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_middle::{bug, span_bug};
-use rustc_span::symbol::sym;
+use rustc_span::sym;
 
 use crate::take_array;