Revert to using different grammar rules for tstring due to format_spec

Author: lysnikolaou

Grammar/python.gram

@@ -916,8 +916,7 @@ fstring_middle[expr_ty]:
     | t=FSTRING_MIDDLE { _PyPegen_constant_from_token(p, t) }
 fstring_replacement_field[expr_ty]:
     | '{' a=annotated_rhs debug_expr='='? conversion=[fstring_conversion] format=[fstring_full_format_spec] rbrace='}' {
-        (TOK_GET_MODE(p->tok)->tstring ? _PyPegen_interpolation : _PyPegen_formatted_value)(
-            p, a, debug_expr, conversion, format, rbrace, EXTRA) }
+        _PyPegen_formatted_value(p, a, debug_expr, conversion, format, rbrace, EXTRA) }
     | invalid_replacement_field
 fstring_conversion[ResultTokenWithMetadata*]:
     | conv_token="!" conv=NAME { _PyPegen_check_fstring_conversion(p, conv_token, conv) }
@@ -929,8 +928,15 @@ fstring_format_spec[expr_ty]:
 fstring[expr_ty]:
     | a=FSTRING_START b=fstring_middle* c=FSTRING_END { _PyPegen_joined_str(p, a, (asdl_expr_seq*)b, c) }
 
+tstring_replacement_field[expr_ty]:
+    | '{' a=annotated_rhs debug_expr='='? conversion=[fstring_conversion] format=[fstring_full_format_spec] rbrace='}' {
+        _PyPegen_interpolation(p, a, debug_expr, conversion, format, rbrace, EXTRA) }
+    | invalid_replacement_field
+tstring_middle[expr_ty]:
+    | tstring_replacement_field
+    | t=FSTRING_MIDDLE { _PyPegen_constant_from_token(p, t) }
 tstring[expr_ty] (memo):
-    | a=TSTRING_START b=fstring_middle* c=FSTRING_END { _PyPegen_template_str(p, a, (asdl_expr_seq*)b, c) }
+    | a=TSTRING_START b=tstring_middle* c=FSTRING_END { _PyPegen_template_str(p, a, (asdl_expr_seq*)b, c) }
 
 string[expr_ty]: s[Token*]=STRING { _PyPegen_constant_from_string(p, s) }
 strings[expr_ty] (memo): a[asdl_expr_seq*]=(fstring|string)+ { _PyPegen_concatenate_strings(p, a, EXTRA) }