Create a new component FSFormula in the shared UI library.

[peyronth]

Task: Create a new component in the shared UI library

The component will be a shared field component named FSFormulaField.

Requirements

• It should be a text-based component with the ability to use variables.
• Variables must be configured through props, just like in FSRichTextField.
• As in FSRichTextField, variables should be treated as single characters and visually distinct from normal text.
• The component must support a modelValue prop and emit updates, where the value is a plain string containing variables inside {}.

Implementation notes

• The FSFormulaField can be based on the same structure as FSRichTextField, using Lexical, but only with the variable mode enabled.
• The rest of the component should behave and look like a FSTextField.
• Ensure conversion from the Lexical object to a plain string without style artifacts.
• Avoid code duplication: factorize reusable parts and aim for clean, robust code with clear responsibilities for each piece.
• Reuse existing elements from the library instead of creating new concepts.