Make copying LMMS' version info easy (easier) by adding text highlighting

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### Enhancement Summary

Copying the version is required for bug reports but not intuitive.

### Implementation Details / Mockup

Right-clicking the version text, selecting "Select all", then right clicking again and selecting "copy" allows to copy the version info. The text does not get highlighted while doing so.


It is very convenient this is possible but not very intuitive when used to
1. being able to double- or triple-click text to select it/the whole line
2. selected text being noticeably highlighted

GIMP, Audacity and Shotcut are examples of software that fulfill the above:

Actually, having tested it a little more, I think selecting/tripleclicking actually works but the lack of highlighting convinced me they don't.

So this is a request then to add noticeable text highlighting for the version info text.

### Please search the issue tracker for existing feature requests before submitting your own.

- [X] I have searched all existing issues and confirmed that this is not a duplicate.

Start by locating the LMMS interface that displays the version information; the issue does not name a file, test, or entry point. Reproduce selecting and copying the version text, then verify that selected text is visibly highlighted and remains copyable as requested.

Written by the indexing model from the issue text.