Delimiter validation updates from JavaScript version

[happy5214]

The Python code includes TagValidator.comma_is_missing_before_opening_bracket(), which is never true in the context in which it is called. The comma validation function TagValidator.find_comma_issues_in_hed_string() also does not flag errors for extra commas or tildes in illegal contexts (e.g. ,, or ,~). I've fixed both in the JavaScript version.

[happy5214]

This expanded delimiter validation is implemented in this JS function. Some tests can be found in this JS code.

The error message now includes the illegal delimiter and the character index of that delimiter in the HED string. The error message is listed as extraDelimiter in https://github.com/VisLab/HEDBidsValid/blob/379fb125028baf3cecfc49989308581d432c646c/utils/issues.js#L12.

[owinterbg]

This issue was addressed in commit 134be8c