package upgrades and consolidation/improvement of build targets checks

There are a few packages that have been deprecated in the meantime, so we should strive to remove/replace where possible. Since we still support netstandard2.0 the remains that are still needed to build those are prepared with Condition attributes in the *.csproj files (until the day comes when we finally can get rid of it)

Additionally, a few #if checks have been found to cause issues in some CI environments, e.g. version specific NETSTANDARD2_0 symbols are only generated for the exact target,, while for all implicit targets only the <framework>_OR_GREATER symbols are defined. The patch consolidates and enhances all of these #if checks to prevent against that.