HSEARCH-3478 + HSEARCH-3425 Code cleanup

[yrodiere]

https://hibernate.atlassian.net//browse/HSEARCH-3425
https://hibernate.atlassian.net//browse/HSEARCH-3478

Note I don't expect a full review, it would be quite boring.

@gsmet, could you simply double-check that the warnings are gone when you use Eclipse? They are gone in my instance of Eclipse, but who knows.
Of course you need to ignore the legacy modules; personally I moved the non-legacy modules to a separate working set, I configured the "Problems" view to only show problems in the selected projects, and I selected the "non-legacy" working set.

[yrodiere]

Note for future reference.

IDEA doesn't offer a global view of all warnings in the codebase, making it difficult to keep the number of warnings to 0. The feature was requested a long time ago and never implemented, so it's unlikely it will ever be: https://youtrack.jetbrains.com/issue/IDEA-68854

Thus I wanted to find some solution to be aware of added warnings and fix them as I code.

I tried to fail the build on warnings by passing -Werror to the compiler, but it seems to stop after the very first warning. Clearly not good.

I also tried to make all warnings appear in IDEA in the "Messages" view, shown when we trigger a full build. That's better than nothing, I thought. Well, no: by passing -Xlint:all to the compiler for non-legacy modules, and -Xlint:none -nowarn for legacy modules, and IDEA correctly detected the options (they appear in the build settings). But for some reason, a lot of warning still appear even for legacy modules. Also, the output seems to include irrelevant warnings, such as warnings we suppressed using @SuppressWarnings, or heap pollution warnings even though we added @SafeVarargs. So we can't control which warnings appear, and there are way too many warnings. Useless.

I'm not going to go back to Eclipse, because even without a global view of warnings, IDEA is still better. And more importantly I won't force people working on Hibernate Search to use one IDE or another.

So... I'm out of idea. I guess we'll have to periodically clean up the codebase...

[coveralls]

Pull Request Test Coverage Report for Build 1

• 194 of 208 (93.27%) changed or added relevant lines in 103 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.5%) to 87.904%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/client/impl/ElasticsearchClientFactoryImpl.java	1	2	50.0%
backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/index/admin/gson/impl/AnalysisJsonElementEquivalence.java	0	1	0.0%
backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/index/admin/impl/ElasticsearchSchemaValidatorImpl.java	2	3	66.67%
backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/orchestration/impl/ElasticsearchSerialChangesetsWorkOrchestrator.java	0	1	0.0%
backend/lucene/src/main/java/org/hibernate/search/backend/lucene/util/impl/AnalyzerUtils.java	8	9	88.89%
engine/src/main/java/org/hibernate/search/engine/common/impl/ErrorContextImpl.java	0	1	0.0%
engine/src/main/java/org/hibernate/search/engine/logging/spi/MappingKeyFormatter.java	0	1	0.0%
engine/src/main/java/org/hibernate/search/engine/spatial/ImmutableGeoPolygon.java	0	1	0.0%
mapper/orm/src/main/java/org/hibernate/search/mapper/orm/cfg/HibernateOrmIndexingStrategyName.java	2	3	66.67%
mapper/orm/src/main/java/org/hibernate/search/mapper/orm/massindexing/impl/MassIndexerImpl.java	2	3	66.67%

Files with Coverage Reduction	New Missed Lines	%
backend/elasticsearch/src/main/java/org/hibernate/search/backend/elasticsearch/gson/impl/UnexpectedJsonElementTypeException.java	1	0.0%
mapper/orm/src/main/java/org/hibernate/search/mapper/orm/bootstrap/impl/HibernateSearchIntegrator.java	1	94.23%

Totals
Change from base Build 136:	0.5%
Covered Lines:	14541
Relevant Lines:	16542

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💛 - Coveralls

[yrodiere]

Approved over the chat. Merged, thanks!