Set output encoding to UTF8

[prafullbhosale]

Fixes #635

cc @mlorbetske

[prafullbhosale]

Rebased from rel/2.0.1 and removed the change for test projects as that's already made in rel/2.0.1.
Will merge this if the CI build is green.

[nbarnwell]

I've just used the following command to re-codegen some RazorPages and noticed they were marked as modified in the solution explorer (I wasn't expecting to see a change). When I looked, the contents matched, but I got the following warning from Visual Studio: "These files have different encodings. Left file: Unicode (UTF-8) with signature. Right file: Western European (Windows). You can resolve the difference by saving the right file with the encoding Unicode (UTF-8) with signature.". Is this related to this issue?

My codegenerator command:
dotnet aspnet-codegenerator razorpage -p Coin.Web -m Budget -dc CoinContext -udl -outDir Areas\Accounting\Pages\Budgets --referenceScriptLibraries --force --no-build