[Concurrent Segment Search] Terms Agg Doc Count Error needs to be calculated across shards instead of slices

[jed326]

Subtask for #7357 to focus on doc count error issues

https://opensearch.org/docs/2.9/aggregations/bucket/terms/

REPRODUCE WITH: ./gradlew 'null' --tests "org.opensearch.search.aggregations.bucket.TermsDocCountErrorIT.testFixedDocs" -Dtests.seed=5B6F53240BBECC6D -Dtests.security.manager=true -Dtests.jvm.argline="-XX:TieredStopAtLevel=1 -XX:ReservedCodeCacheSize=64m" -Dtests.locale=fi -Dtests.timezone=Jamaica -Druntime.java=11

java.lang.AssertionError: 
Expected: <46L>
     but: was <6L>
Expected :<46L>
Actual   :<6L>
<Click to see difference>


	at __randomizedtesting.SeedInfo.seed([5B6F53240BBECC6D:91411370660E073B]:0)
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
	at org.junit.Assert.assertThat(Assert.java:964)
	at org.junit.Assert.assertThat(Assert.java:930)
	at org.opensearch.search.aggregations.bucket.TermsDocCountErrorIT.testFixedDocs(TermsDocCountErrorIT.java:1098)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)