Create LithoReducer.reduce() with immutable inputs and output

Summary:
Following [1/2]:
> Create LithoReducer.reduce() and pull out reduce code from LithoTreeFuture.layout() into it.
LithoReducer.reduce() will take multiple params including the immediateLayoutState and return a LayoutState.

This diff makes a deeper refactor:
- Replace ```layoutState.xx``` in ```LithoReducer``` with ```reductionState.xx``` so that ```layoutState``` won't be mutated
- ```setSizeAfterMeasureAndCollectResults()``` now takes in ```reductionState``` instead of ```layoutState``` as parameter
- ```addRootHostRenderTreeNode()``` is partially migrated to using ```reductionState``` as parameter instead of ```layoutState```

Next Steps:
- Add more test against this change

Reviewed By: pentiumao

Differential Revision: D52832575

fbshipit-source-id: 556599f8e6a1af75f91e31b22f5cd6e4bda8330a

litho-core/src/main/java/com/facebook/litho/LayoutState.java

@@ -161,6 +161,7 @@ public static boolean isFromSyncLayout(@RenderSource int source) {
   private boolean mShouldProcessVisibilityOutputs;
 
   LayoutState(
+      int id,
       ResolveResult resolveResult,
       SizeConstraints sizeConstraints,
       int rootX,
@@ -170,7 +171,7 @@ public static boolean isFromSyncLayout(@RenderSource int source) {
       @Nullable LayoutState current,
       @Nullable LayoutCache.CachedData layoutCacheData,
       ReductionState reductionState) {
-    mId = sIdGenerator.getAndIncrement();
+    mId = id;
     mResolveResult = resolveResult;
     mSizeConstraints = sizeConstraints;
     mRootX = rootX;
@@ -313,6 +314,10 @@ static String layoutSourceToString(@RenderSource int source) {
     }
   }
 
+  static AtomicInteger getIdGenerator() {
+    return sIdGenerator;
+  }
+
   @ThreadSafe(enableChecks = false)
   void preAllocateMountContent(boolean shouldPreallocatePerMountSpec) {
     if (!shouldPreallocatePerMountSpec) {

litho-core/src/main/java/com/facebook/litho/LayoutTreeFuture.kt

@@ -157,7 +157,14 @@ class LayoutTreeFuture(
                   scopedComponentInfosNeedingPreviousRenderData =
                       resolveResult.outputs?.let {
                         ArrayList(it.componentsThatNeedPreviousRenderData)
-                      })
+                      },
+                  c = c,
+                  sizeConstraints = sizeConstraints,
+                  currentLayoutState = currentLayoutState,
+                  root = root,
+                  offsetRootX = lsc.rootOffset.x,
+                  offsetRootY = lsc.rootOffset.y,
+              )
           if (root != null) {
             measurePendingSubtrees(
                 parentContext = c,
@@ -168,16 +175,7 @@ class LayoutTreeFuture(
 
           perfEvent?.markerPoint("start_collect_results")
           val layoutState =
-              LithoReducer.reduce(
-                  lsc,
-                  c,
-                  resolveResult,
-                  sizeConstraints,
-                  treeId,
-                  currentLayoutState,
-                  layoutCache,
-                  root,
-                  reductionState)
+              LithoReducer.reduce(lsc, resolveResult, treeId, layoutCache, reductionState)
           perfEvent?.markerPoint("end_collect_results")
 
           root?.releaseLayoutPhaseData()