Move Theme::Entry definition to top of file

It needs to be at least above this line:

    theme->entries_.reserve(kInitialReserveSize);

Otherwise, after upgrading libc++, the compiler fails with errors about
an incomplete type, e.g.:

include/c++/v1/vector:839:62: error: arithmetic on a pointer to an incomplete type 'android::Theme::Entry'
include/c++/v1/__memory/uninitialized_algorithms.h:609:5: error: cannot increment value of type 'std::reverse_iterator<android::Theme::Entry *>'

Bug: b/175635923
Test: treehugger
Change-Id: I6c231184c3a4c0e67dd29d43560b0c28778883db
diff --git a/libs/androidfw/AssetManager2.cpp b/libs/androidfw/AssetManager2.cpp
index 6523469..edccb8a 100644
--- a/libs/androidfw/AssetManager2.cpp
+++ b/libs/androidfw/AssetManager2.cpp
@@ -91,6 +91,12 @@
   StringPoolRef entry_string_ref;
 };
 
+struct Theme::Entry {
+  ApkAssetsCookie cookie;
+  uint32_t type_spec_flags;
+  Res_value value;
+};
+
 AssetManager2::AssetManager2(ApkAssetsList apk_assets, const ResTable_config& configuration) {
   configurations_.push_back(configuration);
 
@@ -1605,12 +1611,6 @@
 
 Theme::~Theme() = default;
 
-struct Theme::Entry {
-  ApkAssetsCookie cookie;
-  uint32_t type_spec_flags;
-  Res_value value;
-};
-
 base::expected<std::monostate, NullOrIOError> Theme::ApplyStyle(uint32_t resid, bool force) {
   ATRACE_NAME("Theme::ApplyStyle");