[Dogfooding] Enforce IDE0007 (prefer "var") as build warning in IDE projects
[Dogfooding] Enforce IDE0007 (prefer "var") as build warning in IDE projects

```ini
[src/{Analyzers,CodeStyle,Features,Workspaces}/**/*.{cs,vb}]

# Prefer "var" everywhere
dotnet_diagnostic.IDE0007.severity = warning
csharp_style_var_for_built_in_types = true:warning
csharp_style_var_when_type_is_apparent = true:warning
csharp_style_var_elsewhere = true:warning
```

AlekseyTs/roslyn,heejaechang/roslyn,aelij/roslyn,heejaechang/roslyn,wvdd007/roslyn,bartdesmet/roslyn,gafter/roslyn,mgoertz-msft/roslyn,genlu/roslyn,sharwell/roslyn,tmat/roslyn,weltkante/roslyn,panopticoncentral/roslyn,CyrusNajmabadi/roslyn,KirillOsenkov/roslyn,mavasani/roslyn,davkean/roslyn,tannergooding/roslyn,ErikSchierboom/roslyn,KevinRansom/roslyn,davkean/roslyn,KevinRansom/roslyn,physhi/roslyn,mavasani/roslyn,KevinRansom/roslyn,tmat/roslyn,physhi/roslyn,mgoertz-msft/roslyn,shyamnamboodiripad/roslyn,wvdd007/roslyn,eriawan/roslyn,eriawan/roslyn,jmarolf/roslyn,aelij/roslyn,shyamnamboodiripad/roslyn,gafter/roslyn,CyrusNajmabadi/roslyn,jasonmalinowski/roslyn,bartdesmet/roslyn,weltkante/roslyn,tannergooding/roslyn,KirillOsenkov/roslyn,dotnet/roslyn,stephentoub/roslyn,genlu/roslyn,AmadeusW/roslyn,bartdesmet/roslyn,gafter/roslyn,weltkante/roslyn,brettfo/roslyn,jmarolf/roslyn,wvdd007/roslyn,stephentoub/roslyn,tmat/roslyn,eriawan/roslyn,CyrusNajmabadi/roslyn,mavasani/roslyn,mgoertz-msft/roslyn,sharwell/roslyn,panopticoncentral/roslyn,diryboy/roslyn,sharwell/roslyn,brettfo/roslyn,dotnet/roslyn,panopticoncentral/roslyn,stephentoub/roslyn,ErikSchierboom/roslyn,jmarolf/roslyn,jasonmalinowski/roslyn,aelij/roslyn,jasonmalinowski/roslyn,heejaechang/roslyn,davkean/roslyn,ErikSchierboom/roslyn,diryboy/roslyn,genlu/roslyn,AlekseyTs/roslyn,diryboy/roslyn,tannergooding/roslyn,AmadeusW/roslyn,KirillOsenkov/roslyn,physhi/roslyn,AmadeusW/roslyn,shyamnamboodiripad/roslyn,AlekseyTs/roslyn,dotnet/roslyn,brettfo/roslyn