Port ints to qsizetypes where they're not blatantly wrong. This
includes indexed loops that don't require the additional range,
because int these days is a code smell, so if we can save the next
code reader a few moments of digging to convince herself that the int
is ok even in 64-bit builds, then let's do it.
The Windows implementation only has the most obvious occurrences
ported, because I lack platform access. Created QTBUG-105100 to track
the missing changes. OSX should be fine, provided sizeof(long) == 8 on
64-bit OSX.
Pick-to: 6.4 6.3
Task-number: QTBUG-103531
Change-Id: I679183f28ed42e89e2879e29457e6a4e487fed0d
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>