#3998 has regressed VS experience due to changed packageContent.targets,
that no longer could resolve $(IntellisenseXml) variable.
This prevented VS from resolving tooling and dependnecies.
To fix this move all properties within `GetPackageContent` target.
Also run `restore.cmd` before launching VS. This is reqired to ensure
the intellisense bundle, as well as all required SDK and tooling are
downloaded.
This streamlined the DevEx.
Relates to #3998
After repaving I discovered my previous changes weren't correct.
You can't check exists on partial paths. Quoting was wonky, etc.
I've tested this one thoroughly for all three handled states and
it appears to work fine.
Use the developer command prompt VS if available, fall back on devenv
in the path, then finally to file association for .sln.
Normalize casing of the commands.
Igor Velikorossov
Jeremy Kuhne