Update BCP computation to use derive_classpath

We now dynamically compute the classpath during startup so we need to
invoke the 'derive_classpath' program that does this during OTA to
compile everything correctly.

Test: manual OTA on blueline
Bug: 186432034
Change-Id: Iaac6718d8347c671241fbdf08ff79b0a608ad000
diff --git a/cmds/installd/otapreopt_chroot.cpp b/cmds/installd/otapreopt_chroot.cpp
index 83f01de..c62734a 100644
--- a/cmds/installd/otapreopt_chroot.cpp
+++ b/cmds/installd/otapreopt_chroot.cpp
@@ -275,6 +275,7 @@
     static constexpr const std::string_view kRequiredApexs[] = {
       "com.android.art",
       "com.android.runtime",
+      "com.android.sdkext",  // For derive_classpath
     };
     std::array<bool, arraysize(kRequiredApexs)> found_apexs{ false, false };
     DIR* apex_dir = opendir("/apex");