feat: special case AppliedTypeTree in syntax highlighting

This ensure that instead of the entire `List[Int]` all being one color
the `List` is the type color and the `Int` is while the brackets remain
with no color.

Author: ckipp01

compiler/src/dotty/tools/dotc/printing/SyntaxHighlighting.scala

@@ -111,6 +111,11 @@ object SyntaxHighlighting {
             // the braces
             case tree: LambdaTypeTree =>
               tree.tparams.foreach(tparam => highlightPosition(tparam.span, TypeColor))
+            // Also special case these to ensure that each type and arg is
+            // highlighted without the braces.
+            case tree: AppliedTypeTree =>
+              highlightPosition(tree.tpt.span, TypeColor)
+              tree.args.foreach(arg => highlightPosition(arg.span, TypeColor))
             case tree: MemberDef /* ModuleDef | TypeDef */ =>
               highlightAnnotations(tree)
               highlightPosition(tree.nameSpan, TypeColor)

compiler/test/dotty/tools/dotc/printing/SyntaxHighlightingTests.scala

@@ -44,7 +44,7 @@ class SyntaxHighlightingTests extends DottyTest {
     test("type A = String | Int", "<K|type> <T|A> = <T|String> <T||> <T|Int>")
     test("type B = String & Int", "<K|type> <T|B> = <T|String> <T|&> <T|Int>")
     test("type Id[A] = A", "<K|type> <T|Id>[<T|A>] = <T|A>")
-    test("type Foo = [X] =>> List[X]", "<K|type> <T|Foo> = [<T|X>] =>> <T|List[X]>")
+    test("type Foo = [X] =>> List[X]", "<K|type> <T|Foo> = [<T|X>] =>> <T|List>[<T|X>]")
   }
 
   @Test