Add more unit test for bufferhub

TestAsyncStateTransitions
TestZeroConsumer
TestMaxConsumers
TestCreateConsumerWhenBufferGained
TestCreateConsumerWhenBufferPosted
TestCreateConsumerWhenBufferReleased

This also renames the test to buffer_hub-test to match the name scheme
we are using elsewhere (i.e. buffer_hub_xxx instead of bufferhub_xxx and
yyy-test vs yyy_tests).

Bug: 68152849
Test: buffer_hub-test
Change-Id: I18ed32862bbee207e2751139599eff4f6f6e8618
diff --git a/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h b/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
index 1186f93..a356959 100644
--- a/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
+++ b/libs/vr/libbufferhub/include/private/dvr/buffer_hub_client.h
@@ -94,6 +94,9 @@
 
   int id() const { return id_; }
 
+  // Returns the buffer buffer state.
+  uint64_t buffer_state() { return buffer_state_->load(); };
+
   // A state mask which is unique to a buffer hub client among all its siblings
   // sharing the same concrete graphic buffer.
   uint64_t buffer_state_bit() const { return buffer_state_bit_; }