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Closes <https://github.com/emilk/egui/issues/3862>.
Factoring the `bool` members of `Response` into a bitfield, the size of
`Response` is now 96 bytes (down from 104).
I gave `Sense` the same treatment, however this has no effects on
`Response` due to padding. I've decided not to pursue `PointerState`, as
it is quite large (_many_ members that are sized and aligned to
multiples of 8 bytes), so I don't expect any noticeable benefit from
making handful of `bool`s slightly leaner.
In any case, the changes to `Sense` are already quite a bit more
intrusive than those to `Response`.
The previous implementation overloaded the names of the attributes
`click` and `drag` with similarly named methods that _construct_ `Sense`
with the corresponding flag set. Now, that the attributes can no longer
be accessed directly, I had to introduce methods with new names
(`senses_click()`, `senses_drag()` and `is_focusable()`). I don't think
this is the cleanest solution: the old methods are essentially redundant
now that the named constants like `Sense::CLICK` exist. I did however
not want to needlessly break backwards compatibility.
I am happy to revert it (or go further 🙂) if there are concerns.
35860418ac