Create a Conan package for ICU

The CI builds Qt against ICU libraries provisioned on the build machines (linux, win). As the ICU libs may not be present on end users machine the linking against the Qt Conan packages may fail.

The qtbase Conan package should declare a dependency to ICU Conan package. The ICU Conan package should be created and stored in Qt's Conan server which is then also available to customers and opensource users.

The qtbase recipe needs to parse the ICU package version, for the dependency, from the following file which is provisioned for Qt CI:

$HOME/conan_sw_package_versions.ini

[icu-windows]
version = 65.1
[icu-linux]
version = 56.1
[icu-macos]
version = 56.1