Annoying unnecessary logging related to expanding strings that don't require expansion

[andreeis]

Brief Issue Summary

We call the string expansion API on any string we operate with and at the beginning there is a logging mentioning that we're about to transform the content. That happens even for strings that don't contain any varexp pattern and which will remain unchanged, while introducing lots of useless logging lines in the output channel.
Make sure we log anything only when an expansion pattern has been identified.

CMake Tools Diagnostics

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Debug Log

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Additional Information

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