Update install-dotnet and add csc tests

__tests__/csc.test.ts

@@ -0,0 +1,23 @@
+import fs = require('fs');
+
+describe('csc tests', () => {
+  it('Valid regular expression', async () => {
+    var cscFile = require('../.github/csc.json');
+    var regex = cscFile['problemMatcher'][0]['pattern'][0]['regexp'];
+
+    console.log(regex);
+    var re = new RegExp(regex);
+
+    // Ideally we would verify that this
+    var stringsToMatch = [
+      'Program.cs(10,79): error CS1002: ; expected [/Users/zacharyeisinger/Documents/repo/setup-dotnet/__tests__/sample-broken-csproj/sample.csproj]',
+      "S:\\Msbuild\\src\\Build\\Evaluation\\ExpressionShredder.cs(33,7): error CS1003: Syntax error, ',' expected [S:\\msbuild\\src\\Build\\Microsoft.Build.csproj > Properties:prop]"
+    ];
+
+    stringsToMatch.forEach(string => {
+      var matchStr = string.match(re);
+      console.log(matchStr);
+      expect(matchStr).toEqual(expect.anything());
+    });
+  }, 10000);
+});