Removes no longer needed parentheses in @Composable() annotations

-Enables the NonParenthesizedAnnotationsOnFunctionalTypes flag to disable the IDE warning
-Temporarily disables the 'paren-spacing' lint in ktlint, due to: https://github.com/pinterest/ktlint/issues/737
-Turns unnecessary parentheses into a 'warning', and stops ignoring this IDE inspection in the UI project

Bug: b/155391691
Test: ./gradlew bOS, Studio
Change-Id: Ib4af53591b82a0d56ae0733ff2561196c2d49635

diff --git a/ui/ui-foundation/src/androidTest/java/androidx/ui/foundation/ScrollableTest.kt b/ui/ui-foundation/src/androidTest/java/androidx/ui/foundation/ScrollableTest.kt
index 91ef177..27dfc12 100644
--- a/ui/ui-foundation/src/androidTest/java/androidx/ui/foundation/ScrollableTest.kt
+++ b/ui/ui-foundation/src/androidTest/java/androidx/ui/foundation/ScrollableTest.kt

@@ -572,7 +572,7 @@
         }
     }
 
-    private fun setScrollableContent(scrollableModifierFactory: @Composable() () -> Modifier) {
+    private fun setScrollableContent(scrollableModifierFactory: @Composable () -> Modifier) {
         composeTestRule.setContent {
             Stack {
                 val scrollable = scrollableModifierFactory()