Simplify preview warning

[nguerrera]

Replaces #2198

[nguerrera]

cc @KathleenDollard @livarcocc @richlander Moved rich's commit onto 2.1.4xx, resolved merge conflict with error codes, and updated XLF.

[dsplaisted]

@richlander The aka.ms link here redirects to https://docs.microsoft.com/en-us/dotnet/core/tools/global-json, which is just a generic global.json reference. Is that the intent or will there be a different page more specific to .NET Core previews?

[nguerrera]

cc @mairaw

[mairaw]

Microsoft's style guide asks for contractions (https://docs.microsoft.com/en-us/style-guide/word-choice/use-contractions):
You are -> You're

@dsplaisted I wasn't aware of that link going to our topic until a customer got confused with that page after getting this message. I was just planning to add a Troubleshooting area to that topic to explain some warnings you might get and what to do. There's also a warning from EF projects that are redirected to that same topic.

However, this simplification makes the warning even more cryptic in my opinion.

[nguerrera]

Do we still want to take this change, then?

[dsplaisted]

I think we should either add back a sentence along the lines of "You can define the SDK version via a global.json file in the current project.", or create a more specific page for https://aka.ms/dotnet-core-preview to point to.

[mairaw]

That page is getting expanded dotnet/docs#4704

[dsplaisted]

That page is getting expanded dotnet/docs#4704

Given those updates to the target of the link, I think the message in this PR is OK.

[KathleenDollard]

I'm fine with @dsplaisted 's suggested resolution here.