[NEW TOOL] RegEx Build and Test

[wuergezwerg]

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It would be nice to have a "RegEx Build and Test" tool similar to https://regexr.com/. It really helps to create regex when you only need it once every 2 months. The option to look at the different expressions in the cheatsheet helps to remember also :D

[Nezteb]

Duplicate of https://github.com/CorentinTh/it-tools/issues/308 (which technically came first), though this issue's [NEW TOOL] is the correct prefix. 😄

[sharevb]

Hi @wuergezwerg and @CorentinTh, implemented in #1030