GeezerVison

A decorator with a dotted name was parsed into a single Name whose Id is the whole dotted string, so @decorators.author('Cleese') fails at runtime with NameError: name 'decorators.author' is not defined.

CPython 3.4 (ast_for_decorator / ast_for_dotted_name in Python/ast.c) builds Name(a) plus one Attribute(..., Load) per further component, all positioned at the start of the dotted name, and wraps that in a Call when there are arguments. The decorator rule now builds the same Name / Attribute chain through a small dottedName helper. Plain decorators also get the name's position instead of the @ (col 1 for @foo), as in CPython.

The helper is in parser.go rather than the grammar.y prologue so grammar.y keeps its line numbers: the regenerated y.go changes by one line and y.output not at all.

Tests:

• vm/tests/decorators.py: enabled test_dotted and test_eval_order from CPython's test_decorators.py (both were commented out), and the nullval.attr case now expects AttributeError, as in CPython. All three fail on main with NameError.
• parser: added dotted decorator cases to make_grammar_test.py and grammar_data_test.go (on a function, with call args, stacked on a class, and @a. staying a SyntaxError). No python3.4 here, so the new rows were written by hand in the generator's output format and cross-checked against CPython's ast.
• go test -race ./... passes on Go 1.18, 1.19 and 1.27.

Fixes #264.