Fix #2218. Prevent insertion of duplicate characters for * and $

[jeffslofish]

Description

Prevent insertion of duplicate characters for * and $. So when the user types *, just * appears instead of **. Likewise for $.

Issue fixed

#2218

Type of changes

• ☑️ Bug fix (Change that fixed an issue)
• ☑️ Breaking change (Change that can cause existing functionality to change)
• ⚪ Improvement (Change that improves the code. Maybe performance or development improvement)
• ⚪ Feature (Change that adds new functionality)
• ⚪ Documentation change (Change that modifies documentation. Maybe typo fixes)

Checklist:

• ☑️ My code follows the project code style
• ⚪ I have written test for my code and it has been tested
• ⚪ All existing tests have been passed
• ⚪ I have attached a screenshot/video to visualize my change if possible

[ZeroX-DG]

Thank you for your contribution but some users may still want that functionality so I think we'll use this PR #2689. But thank you for your contribution.