This allows list items to built from component parts as required, and additional
functionality is added:
* Icons and text can be positioned at the start or end of the space (templated.)
* Font size of text can be changed (templated.)
* Palette of sprites can be set (runtime.)
This simplifies processing nwidget parts as, unlike the remaining length, the pointer to the end of the list never changes. This is the same principle as we use(d) for tracking end instead of length for C-style strings.
And this removes 160~ instances of the lengthof() macro.
Having to choose between DropDownListStringItem, DropDownListCharStringItem, and DropDownListParamStringItem depending on whether to draw a StringID, a raw string, or a StringID with extra parameters was needlessly complex.
Instead, allow passing a StringID or raw string to DropDownListStringItem. This will preformat the StringID into a raw string, and can therefore accept parameters via the normal SetDParam mechanism.
This also means that strings no longer need to be formatted on every draw.
Since dropdown menus now get closed if they lose focus, 'instant close' dropdowns (i.e. the toolbar dropdowns) should no longer execute their action to avoid unintended actions.
Clicking and releasing on the query toolbar icon is meant to select the land-info tool.
This did not work as during closing a window, OnFocusLost() is called, which then closes the window again. These two calls toggled the land-info tool one and off in the same action.
Resolve by not calling Window::Close in OnFocusLost() if the window is already closing.
Since dropdowns self-close, the detection of re-clicking a dropdown
button no longer worked, as the dropdown is already closed.
Instead set (and then test) a flag on the parent widget to indicate that
the dropdown closed. This method avoids looping windows on every click.
Dropdowns which are taller than the main window should automatically have
a scrollbar added. This did not work for toolbar dropdown as the location
near the top of the window resulted in an unsigned underflow.
This happens if the bounding dimensions are changed so that each item is the same size, as happens on the railtype/roadtype dropdown lists, as the vertical offset was calculated before this dimension is changed.
DropDownListItem are strongly managed using std::unique_ptr to ensure leak-free handling. Appropriate use
of move-semantics make intent a lot clearer than parameter comments and allows the compiler to generate
copy-free code for most situations.
