Add error handling do detect when MSBuild 14 is missing
Add error handling do detect when MSBuild 14 is missing

The code formatter currently just crashes with a type load exception
if the MSBuild 14 is missing. Instead, it's better to detect this
case and provide an actionable error message.

jeremyabbott/codeformatter,BertTank/codeformatter,rollie42/codeformatter,weltkante/codeformatter,michaelcfanning/codeformatter,Maxwe11/codeformatter,shiftkey/codeformatter,jaredpar/codeformatter,dotnet/codeformatter,cbjugstad/codeformatter,dotnet/codeformatter,david-mitchell/codeformatter,BradBarnich/codeformatter,srivatsn/codeformatter,shiftkey/Octokit.CodeFormatter,twsouthwick/codeformatter,twsouthwick/codeformatter,hickford/codeformatter,mmitche/codeformatter,mmitche/codeformatter,rainersigwald/codeformatter,kharaone/codeformatter