[clang-format] Handle commas in [] in C#

[jbcoe]

Summary

Respect setting SpacesInSquareBrackets for commas in square brackets in C# code.

clang/lib/Format/TokenAnnotator.cpp

if (Style.isCpp()) {
     // Spaces around '=>'.
     if (Left.is(TT_JsFatArrow) || Right.is(TT_JsFatArrow))
       return true;
 
     // space between type and variable e.g. Dictionary<string,string> foo;
     if (Left.is(TT_TemplateCloser) && Right.is(TT_StartOfName))
       return true;
 
+    // space after comma in '[,]'.
+    if (Left.is(tok::comma) && Right.is(tok::r_square))
+      return Style.SpacesInSquareBrackets;
+
     // 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"(new Car { someVariableName })", Style);
   verifyFormat(R"(new Car { someVariableName })", Style);
   verifyFormat(R"(new Dictionary<string, string> { ["Key"] = "Value" };)",
                Style);
   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);
+
+  Style.SpacesInSquareBrackets = true;
+  verifyFormat(R"(private float[, ] Values;)", Style);
 }
 
 } // namespace format
 } // end namespace clang