Update solutions to VS 2019

EFCore.Cosmos.sln

@@ -1,8 +1,8 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 15
-VisualStudioVersion = 15.0.27713.0
-MinimumVisualStudioVersion = 15.0.26730.03
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28418.106
+MinimumVisualStudioVersion = 16.0.28418.106
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{712F6813-A5CD-40D4-836F-F9667A3AE762}"
 	ProjectSection(SolutionItems) = preProject
 		src\EFCore.ruleset = src\EFCore.ruleset

EFCore.Runtime.sln

@@ -1,8 +1,8 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 15
-VisualStudioVersion = 15.0.27130.2027
-MinimumVisualStudioVersion = 15.0.26730.03
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28418.106
+MinimumVisualStudioVersion = 16.0.28418.106
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{F6F469BA-DCFA-4A88-958D-A4A91FCDF8B1}"
 	ProjectSection(SolutionItems) = preProject
 		.editorconfig = .editorconfig

EFCore.sln

@@ -2,7 +2,7 @@
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 16
 VisualStudioVersion = 16.0.28418.106
-MinimumVisualStudioVersion = 15.0.26730.03
+MinimumVisualStudioVersion = 16.0.28418.106
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "samples", "samples", "{C41FD56B-38CD-40E3-89E6-071A6C58E36C}"
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{B9E4CC99-199C-4E3B-9EC5-D1FDFCD6C27B}"

Microsoft.Data.Sqlite.sln

@@ -1,8 +1,8 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio 15
-VisualStudioVersion = 15.0.27004.2005
-MinimumVisualStudioVersion = 15.0.26730.03
+# Visual Studio Version 16
+VisualStudioVersion = 16.0.28418.106
+MinimumVisualStudioVersion = 16.0.28418.106
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{9396F8F4-299D-427C-B829-EF9A931DAA3C}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Data.Sqlite.Core", "src\Microsoft.Data.Sqlite.Core\Microsoft.Data.Sqlite.Core.csproj", "{2D5D31C9-4BE6-432E-B3C3-351A7A65353D}"

startvs.cmd

@@ -11,9 +11,6 @@ SET DOTNET_MULTILEVEL_LOOKUP=0
 :: Put our local dotnet.exe on PATH first so Visual Studio knows which one to use
 SET PATH=%DOTNET_ROOT%;%PATH%
 
-:: Needed for VS 2017 to find the SDK
-SET MSBuildSDKsPath=%DOTNET_ROOT%sdk\3.0.100-preview-010010\Sdks
-
 SET sln=%1
 
 IF NOT EXIST "%DOTNET_ROOT%\dotnet.exe" (