Create "expand/collapse button with label".

[pixelzoom]

In phetsims/fourier-making-waves#254, we identified a need for a "expand/collapse button with label" in order to properly support alt input features. For example:

Clicking on either the button or label should toggle the Property associated with the ExpandCollapseButton.

Focus highlight should surround both the button and label, and tab traversal should not visit the ExpandCollapseButton invidually.

Interactive highlight should similarly surround both the button and label.

This is not blocking for phetsims/fourier-making-waves#254.

Note that fourier-making-waves currently includes LabeledExpandCollapseButton, which might be used as a starting point -- but the label should be generalized to any type of Node. Creating such a subclass seems preferrable to adding yet-another option to ExpandCollapseButton.