Show parser errors on UI

As a User of T-RegEx, I want to be informed about errors in my regular expression, to be able to recognize errors and understand why no matches are displayed.

Satisfied if:

Errors are shown to the user
If an error exists, a ❗ is shown
On hover on the ❗ a tooltip is shown with the error

Edited Mar 10, 2021 by Pascal Meissner

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