Merge recent doc changes for OEMCrypto

This is a cherry pick of recent changes to OEMCrypto and ODK. Most of
these are part of the document migration to doxygen.

See http://go/wvgerrit/106005 and its parents for code reviews.

Bug: 144715340
Bug: 148232693
Bug: 167580674
Change-Id: I658f99c8117b974faed97322d61fac0f382283af

libwvdrmengine/oemcrypto/ref/src/oemcrypto_engine_ref.cpp

@@ -23,6 +23,14 @@
 #include "oemcrypto_rsa_key_shared.h"
 #include "string_conversions.h"
 
+namespace {
+
+// Lower bits in SessionId are actual session id. The rest higher bits are
+// session type.
+const uint32_t kSessionIdTypeShift = 28;
+const uint32_t kSessionIdMask = (1u << kSessionIdTypeShift) - 1u;
+}  // namespace
+
 namespace wvoec_ref {
 
 // Note: The class CryptoEngine is configured at compile time by compiling in
@@ -64,6 +72,12 @@ SessionId CryptoEngine::OpenSession() {
   std::unique_lock<std::mutex> lock(session_table_lock_);
   static OEMCrypto_SESSION unique_id = 1;
   SessionId id = ++unique_id;
+  // Check if too many sessions have been opened.
+  if (SessionTypeBits(id) != 0) {
+    return 0;
+  }
+  // Apply session type to higher bits.
+  id = (kSessionTypeOEMCrypto << kSessionIdTypeShift) | (id & kSessionIdMask);
   sessions_[id] = MakeSession(id);
   return id;
 }
@@ -251,4 +265,8 @@ OEMCryptoResult CryptoEngine::SetDestination(
   return OEMCrypto_SUCCESS;
 }
 
+uint32_t CryptoEngine::SessionTypeBits(SessionId sid) {
+  return sid >> kSessionIdTypeShift;
+}
+
 }  // namespace wvoec_ref