This enables "classic" desktop builds of ICU4C for both ARM (32-bit)
and ARM64 (64-bit) on Windows.
All but the two samples "cal" and "date" in the "allinone" project now
have ARM and ARM64 project configurations, and build for Windows Desktop
ARM/ARM64.
Note: In order to build the ARM/ARM64 data DLL, you need to first build
x64/Release, as the ARM/ARM build uses the x64 bits in order to be able
to cross-compile for ARM/ARM64. This allows for completely building
ARM/ARM64 binaries using only x64 hardware.
The ARM/ARM64 builds require using a newer version of the Windows SDK
than 8.1, so they have a separate WindowsTargetPlatformVersion which
uses Windows 10 SDK version 10.0.16299.0 (aka RS3), which is the first
version of the Windows SDK to support building ARM64 desktop applications.
In addition this also greatly cleans-up the ICU4C ".vcxproj" files, in
order to remove redundant parts, fix inconsistencies, and make them more
readable. This introduces two new variables in the shared `*.props`
files: `IcuBinOutputDir` and `IcuLibOutputDir` in order to further
reduce the amount of duplicated lines in the individual ".vcxproj"
files themselves.
