AAPT2: Ensure style strings are always first in StringPool

Move the styled strings to a separate section of the StringPool so
that sorting can never mess up the order of Styles.

Bug: 63570514
Test: make aapt2_tests
Change-Id: Id2ce1355b92be1bb31ce0daa7e54ae9b5b6c2ffe
diff --git a/tools/aapt2/ResourceParser_test.cpp b/tools/aapt2/ResourceParser_test.cpp
index d47a529..1683c64 100644
--- a/tools/aapt2/ResourceParser_test.cpp
+++ b/tools/aapt2/ResourceParser_test.cpp
@@ -117,7 +117,7 @@
   StyledString* str = test::GetValue<StyledString>(&table_, "string/foo");
   ASSERT_THAT(str, NotNull());
 
-  EXPECT_THAT(*str->value->str, Eq("This is my aunt\u2019s fickle string"));
+  EXPECT_THAT(str->value->value, Eq("This is my aunt\u2019s fickle string"));
   EXPECT_THAT(str->value->spans, SizeIs(2));
   EXPECT_THAT(str->untranslatable_sections, IsEmpty());
 
@@ -190,7 +190,7 @@
 
   StyledString* str = test::GetValue<StyledString>(&table_, "string/foo");
   ASSERT_THAT(str, NotNull());
-  EXPECT_THAT(*str->value->str, Eq("There are %1$d apples"));
+  EXPECT_THAT(str->value->value, Eq("There are %1$d apples"));
   ASSERT_THAT(str->untranslatable_sections, SizeIs(1));
 
   // We expect indices and lengths that span to include the whitespace