8372348: Adjust some UL / JFR string deduplication output messages

[MBaesken]

There is some UL output in the string deduplication code that is not very clear and has room for improvement.
The inspected strings number should be shown and the new unknown strings get a changed text.
(also the new JFR strip dedup event description is slightly adjusted)

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Issue

• JDK-8372348: Adjust some UL / JFR string deduplication output messages (Enhancement - P4)

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