Add ambivalent expressions to metadata

[jansule]

Feature Request

Is your feature request related to a problem? Please describe.

Some mapbox expressions do not have a clear 1:1 relationship with expressions in geostyler-style. E.g. the e expression (https://github.com/geostyler/geostyler-mapbox-parser/blob/beta-4/src/Expressions.ts#L200). This might lead to ambivalence when parsing there and back.

Describe the solution you'd like

It might be helpful to add those expressions to the metadata so that we maintain a bijective relation between mapbox style and geostyler-style.

Describe alternatives you've considered
None

Additional context
None