[docs] [issue41224] Document is_annotate() in symtable and update doc strings

Change by Andrés Delfino : ---------- nosy: +adelfino nosy_count: 2.0 -> 3.0 pull_requests: +22838 pull_request: https://github.com/python/cpython/pull/23861 _______________________________________ Python tracker https://bugs.python.org/issue41224 _______________________________________