Rewrite & optimize LimitedQueue (#3798)

* Use circular buffer for LimitedQueue

* Reduce copying of snapshot

* Small optimizations

* Remove unneeded lock statements

* Add LimitedQueue tests

* Fix includes for limited queue benchmark

* Update CHANGELOG.md

* Use correct boost version iterators

* Use a shared_mutex to clarify reads and writes

* Update `find`/`rfind` to return the result as a boost::optional

* Use `[[nodiscard]]` where applicable

* Update comments

* Add a couple more doc comments

* Replace size with get

get is a safe (locked & checked) version of at

* Use std::vector in LimitedQueueSnapshot

* Update LimitedQueue benchmarks

* Add mutex guard to buffer accessors

We do not know whether T is an atomic type or not
so we can't safely say that we can copy the value
at a certain address of the buffer.

See https://stackoverflow.com/a/2252478

* Update doc comments, add first/last getters

* Make limit_ const

* Omit `else` if the if-case always returns

* Title case category comments

* Remove `at`

* Fix `get` comment

* Privatize/comment/lock property accessors

 - `limit` is now private
 - `space` is now private
 - `full` has been removed
 - `empty` now locks

* Remove `front` function

* Remove `back` method

* Add comment to `first`

* Add comment to `last`

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/widgets/Scrollbar.hpp

@@ -67,7 +67,7 @@ protected:
 private:
     Q_PROPERTY(qreal currentValue_ READ getCurrentValue WRITE setCurrentValue)
 
-    LimitedQueueSnapshot<ScrollbarHighlight> getHighlightSnapshot();
+    LimitedQueueSnapshot<ScrollbarHighlight> &getHighlightSnapshot();
     void updateScroll();
 
     QMutex mutex_;