feat: add fields in except_clause

Author: amaanq

Diff for: grammar.js

@@ -359,10 +359,10 @@ module.exports = grammar({
     except_clause: $ => seq(
       'except',
       optional(seq(
-        $.expression,
+        field('value', $.expression),
         optional(seq(
           choice('as', ','),
-          $.expression,
+          field('alias', $.expression),
         )),
       )),
       ':',

Diff for: test/corpus/statements.txt

@@ -515,21 +515,21 @@ finally:
       (expression_statement
         (identifier)))
     (except_clause
-      (identifier)
+      value: (identifier)
       (block
         (expression_statement
           (identifier))))
     (except_clause
-      (as_pattern
+      value: (as_pattern
         (identifier)
         alias: (as_pattern_target
           (identifier)))
       (block
         (expression_statement
           (identifier))))
     (except_clause
-      (identifier)
-      (identifier)
+      value: (identifier)
+      alias: (identifier)
       (block
         (expression_statement
           (identifier))))
@@ -542,7 +542,7 @@ finally:
       (expression_statement
         (identifier)))
     (except_clause
-      (identifier)
+      value: (identifier)
       (block
         (expression_statement
           (identifier))