[ENGINE] Fix updates dynamic settings in InternalEngineHolder

After the refactoring in #8784 some settings didn't get passed to the
actual engine and there exists a race if the settings are updated while
the engine is started such that the actual starting engine doesn't see
the latest settings. This commit fixes the concurrency issue as well as
adds tests to ensure the settings are reflected.

Conflicts:
	src/main/java/org/elasticsearch/index/engine/internal/InternalEngine.java
	src/main/java/org/elasticsearch/index/engine/internal/InternalEngineHolder.java
	src/test/java/org/elasticsearch/index/engine/internal/InternalEngineTests.java