Id clashes can cause subtle bugs.
egui already warns when the same Id is used to interact with different
parts of the screen.
This adds warnings about id clashes for some widgets that store state:
Grid, Plot, ScrollArea, Table.
The PR also adds `Context::check_for_id_clash` so users who create
their own widgets can add the same type of check.
* Clip by default
* Fix some spacing bugs
* datepicker: look nicer in light mode
* datepicker: show month names
* Table: don't allow resize of last column if it is Size::Remainder
* Let 1D strips fill up parent width/height
* Add Strip + Table + DatePicker to egui_extras changelog
* Expose some dragging- and pointer related context/memory methods
* Make tables resizable
