Disable a few Visual Studio warnings:
C4244: conversion from 'type1' to 'type2', possible loss of data
C4267: conversion from 'size_t' to 'type', possible loss of data
Considering the GCC/Clang counterpart '-Wconversion'
(https://gcc.gnu.org/wiki/NewWconversion) is not covered by '-Wall', it
seems to make more sense to disable these two warnings in Visual Studio,
rather than fixing these warnings with hundreds of static_cast<> in the
source code.
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