libcompositionengine: avoid vector<const T>

A container of const T uses std::allocator<const T>, which was an
undocumented libc++ extension that has been removed.

See llvm/llvm-project#96319.

Bug: 349681543
Test: m libcompositionengine
Change-Id: I359350a298fc9a59c0ca925a36f753ac3fb3b64e

Author: rprichard

services/surfaceflinger/CompositionEngine/include/compositionengine/impl/planner/Predictor.h

@@ -92,15 +92,15 @@ class LayerStack {
     }
 
 private:
-    std::vector<const LayerState> copyLayers(const std::vector<const LayerState*>& layers) {
-        std::vector<const LayerState> copiedLayers;
+    std::vector<LayerState> copyLayers(const std::vector<const LayerState*>& layers) {
+        std::vector<LayerState> copiedLayers;
         copiedLayers.reserve(layers.size());
         std::transform(layers.cbegin(), layers.cend(), std::back_inserter(copiedLayers),
                        [](const LayerState* layerState) { return *layerState; });
         return copiedLayers;
     }
 
-    std::vector<const LayerState> mLayers;
+    std::vector<LayerState> mLayers;
 
     // TODO(b/180976743): Tune kMaxDifferingFields
     constexpr static int kMaxDifferingFields = 6;