Rename all ParseSess variables/fields/lifetimes as psess.

Existing names for values of this type are `sess`, `parse_sess`,
`parse_session`, and `ps`. `sess` is particularly annoying because
that's also used for `Session` values, which are often co-located, and
it can be difficult to know which type a value named `sess` refers to.
(That annoyance is the main motivation for this change.) `psess` is nice
and short, which is good for a name used this much.

The commit also renames some `parse_sess_created` values as
`psess_created`.

compiler/rustc_interface/src/util.rs

@@ -369,7 +369,7 @@ pub(crate) fn check_attr_crate_type(
                 // by the time that runs the macro is expanded, and it doesn't
                 // give an error.
                 validate_attr::emit_fatal_malformed_builtin_attribute(
-                    &sess.parse_sess,
+                    &sess.psess,
                     a,
                     sym::crate_type,
                 );