FormatOps: outindent after fewer braces in infix

When a fewer braces call is used before an infix operator, that operator
may not be indented as it will otherwise be interpreted as part of the
fewer-braces argument.

This fix leaves a few cases (notably, many for newlines.source=unfold)
still broken, but that requires a change to the parser which will be
released in the new version of scalameta.

scalafmt-core/shared/src/main/scala/org/scalafmt/internal/FormatOps.scala

@@ -485,7 +485,8 @@ class FormatOps(
             case x => !isEnclosedInParens(x)
           })
         val afterInfix = style.breakAfterInfix(t)
-        if (afterInfix ne Newlines.AfterInfix.keep) {
+        if (isBeforeOp && endsWithFewerBraces(app.lhs)) Seq(Split(Newline, 0))
+        else if (afterInfix ne Newlines.AfterInfix.keep) {
           if (isBeforeOp) Seq(Split(Space, 0))
           else {
             val spaceMod = Space(useSpace)

scalafmt-core/shared/src/main/scala/org/scalafmt/util/TreeOps.scala

@@ -1019,4 +1019,16 @@ object TreeOps {
   def isFewerBraces(tree: Term.Apply)(implicit dialect: Dialect): Boolean =
     dialect.allowFewerBraces && tree.argClause.tokens.head.is[Colon]
 
+  @tailrec
+  def endsWithFewerBraces(tree: Tree)(implicit dialect: Dialect): Boolean =
+    tree match {
+      case t: Term.Apply => isFewerBraces(t)
+      case t: Term.ApplyInfix =>
+        t.argClause.values match {
+          case arg :: Nil => endsWithFewerBraces(arg)
+          case _ => false
+        }
+      case _ => false
+    }
+
 }