* fix issue #20922 by handling missing expr in `exprList` for `tkOf`
* fix line numbers in test case
* rewrite exprList requiring expr, add optionalExprList for except
As suggested by @metagn.
* update test case to reflect new code
* update grammar.txt
* update line numbers in test case taking into account nimout
Given the number of errors that are produced it seems easier to do it
this way instead of using `tt.Error`.