AAPT2: Share split functionality between link and optimize

Generating splits should be possible to do from the optimize command.
This means that a lot of infrastructure around split APKs can be
shared by both the optimize and link phase.

Bug: 35925830
Change-Id: Ia88b9e4bff300a56353b2f7a4a2547c8eb43a299
Test: manual
diff --git a/tools/aapt2/Main.cpp b/tools/aapt2/Main.cpp
index 36c1de6..87fda16 100644
--- a/tools/aapt2/Main.cpp
+++ b/tools/aapt2/Main.cpp
@@ -25,7 +25,7 @@
 static const char* sMajorVersion = "2";
 
 // Update minor version whenever a feature or flag is added.
-static const char* sMinorVersion = "12";
+static const char* sMinorVersion = "13";
 
 int PrintVersion() {
   std::cerr << "Android Asset Packaging Tool (aapt) " << sMajorVersion << "."