Replace user-specified empty constructors and destructors with the
compiler-generated versions, which has a number of advantages for code
generation, in addition to being more clear.
Closes#22965.
Closes#24058.
This simple class has a collapsed state which is indicated by a small button and a label. It is now used in the generic implementation of wxCollapsiblePane.
It could be used in more complex layouts than wxCollapsiblePane and is therefore available and documented to the user.