Containers are always fixed to the pixel grid so position and size them
with integers instead of doubles.
Functionally this should be no different since rounding down is already
being done on things like layout. But it makes it clear what the
intention is and avoids bugs where fractional pixels are used. The
translating and moving code is still using doubles because the cursors
can have fractional pixels and thus the code is plumbed that way. But
that could also probably be changed easily by doing the integer
conversions earlier and plumbing with int.
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