Print regions in type_name.

Currently they are skipped, which is a bit weird, and it sometimes
causes malformed output like `Foo<>` and `dyn Bar<, A = u32>`.

Most regions are erased by the time `type_name` does its work. So all
regions are now printed as `'_` in non-optional places. Not perfect, but
better than the status quo.

`c_name` is updated to trim lifetimes from MIR pass names, so that the
`PASS_NAMES` sanity check still works. It is also renamed as
`simplify_pass_type_name` and made non-const, because it doesn't need
to be const and the non-const implementation is much shorter.

The commit also renames `should_print_region` as
`should_print_optional_region`, which makes it clearer that it only
applies to some regions.

Fixes rust-lang#145168.

Author: nnethercote

core/src/any.rs

@@ -835,9 +835,9 @@ impl fmt::Debug for TypeId {
 ///
 /// The returned string must not be considered to be a unique identifier of a
 /// type as multiple types may map to the same type name. Similarly, there is no
-/// guarantee that all parts of a type will appear in the returned string: for
-/// example, lifetime specifiers are currently not included. In addition, the
-/// output may change between versions of the compiler.
+/// guarantee that all parts of a type will appear in the returned string. In
+/// addition, the output may change between versions of the compiler. For
+/// example, lifetime specifiers were omitted in some earlier versions.
 ///
 /// The current implementation uses the same infrastructure as compiler
 /// diagnostics and debuginfo, but this is not guaranteed.