Add expression parsing for numeric inputs

[Nidrax]

Is your feature request related to a problem? Please describe

n/a

Describe the solution you'd like

Add the ability to insert mathematical expressions in textboxes for width, height, brush size etc. where this seems reasonable.
Also: consider the string length (current len for textboxes: 8 chars)

Describe alternatives you've considered

No response

Additional context

https://github.com/codeplea/tinyexpr