[clang-format] insert space after C# keyword var in var (key, value)

[MyDeveloperDay]

LGTM, thank you

clang/lib/Format/TokenAnnotator.cpp

if (Style.isCpp()) {
     // No space between consecutive commas '[,,]'.
     if (Left.is(tok::comma) && Right.is(tok::comma))
       return false;
 
     // Possible space inside `?[ 0 ]`.
     if (Left.is(TT_CSharpNullConditionalLSquare))
       return Style.SpacesInSquareBrackets;
 
+    // space after var in `var (key, value)`
+    if (Left.is(Keywords.kw_var) && Right.is(tok::l_paren))
+      return true;
+
     // space between keywords and paren e.g. "using ("
     if (Right.is(tok::l_paren))
       if (Left.isOneOf(tok::kw_using, Keywords.kw_async, Keywords.kw_when))
         return Style.SpaceBeforeParens == FormatStyle::SBPO_ControlStatements ||
                spaceRequiredBeforeParens(Right);
   } else if (Style.Language == FormatStyle::LK_JavaScript) {
     if (Left.is(TT_JsFatArrow))
       return true;

clang/unittests/Format/FormatTestCSharp.cpp

TEST_F(FormatTestCSharp, CSharpSpaces) {
   verifyFormat(R"(Apply(x => x.Name, x => () => x.ID);)", Style);
   verifyFormat(R"(bool[] xs = { true, true };)", Style);
   verifyFormat(R"(taskContext.Factory.Run(async () => doThing(args);)", Style);
   verifyFormat(R"(catch (TestException) when (innerFinallyExecuted))", Style);
   verifyFormat(R"(private float[,] Values;)", Style);
   verifyFormat(R"(Result this[Index x] => Foo(x);)", Style);
 
   verifyFormat(R"(char[,,] rawCharArray = MakeCharacterGrid();)", Style);
+  verifyFormat(R"(var (key, value))", Style);
 
   // Not seen as a C-style cast.
   verifyFormat(R"(//
 foreach ((A a, B b) in someList) {
 })",
                Style);
 
   Style.SpacesInSquareBrackets = true;