Formatter: do not use a space when using < and > for a map literal.

pkg/analyzer/test/services/data/style_guide_tests.data

 >>> DO use ; instead of {} for empty constructor bodies
 class Point {
   int x, y;
   Point(this.x, this.y) {}
 }
 <<<
 class Point {
   int x, y;
   Point(this.x, this.y);
 }
@@ skipping 135 matching lines @@
 
   try {
     flow();
   } catch (e) {
     print(e);
   }
 }
 >>> DON'T use a space after (, [, and {, or before ), ], and }.
 spaces() {
   var numbers = <int> [ 1, 2,( 3+4 ) ];
+  var mapLiteral = <int, int> {};
 }
 <<<
 spaces() {
   var numbers = <int>[1, 2, (3 + 4)];
+  var mapLiteral = <int, int>{};
 }
 >>> DO use a space before { in function and method bodies.
 getEmptyFn(a){
   return (){};
 }
 <<<
 getEmptyFn(a) {
   return () {};
 }
 >>> DO format constructor initialization lists with each field on its own line.
@@ skipping 45 matching lines @@
   }
 }
 >>> DO use four spaces for method cascades
 var list = new List()
   ..addAll([1, 2, 3])
   ..addAll([4, 5, 6]);
 <<<
 var list = new List()
     ..addAll([1, 2, 3])
     ..addAll([4, 5, 6]);