Add functions to modify the placeholder values

[mrozanc]

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This feature adds functions to modify the placeholder values.

Originally I wanted to use the distance value from distanceOrZero from this first PR to increment a value from a custom capture group, but it was not possible.

I saw an opportunity to solve a lot of use cases by adding functions to the placeholders instead, including this one: https://github.com/qoomon/maven-git-versioning-extension/issues/246.

In my pipeline this would allow me to increment the pre-release part from RCs tags like 1.2.3-rc.2.