Update constructors and create functions

Problem/Motivation

Constructors become part of an object's public API, but often change as functionality gets added, which in turn generates complexity in the constructor, e.g.: having to declare nullable new parameters at the end, having unused arguments, etc.

Since Elasticsearch Connector major versions (i.e.: release series') follow Elasticsearch's major versions, it may be impossible to introduce breaking changes until Elasticsearch itself releases a new version.

Given that constructors are part of the public API, and we can't introduce breaking changes easily, the potential for complex cruft to build up in them over the lifecycle of an Elasticsearch Connector release series is higher than other modules which don't follow an upstream project's release series as closely.

Fortunately, if we do dependency injection using \Drupal\Core\Plugin\ContainerFactoryPluginInterface::create(), then we can change private/protected properties of an object in the create() function, because the create function is in the same class.

Note, however, that there are a few places where we cannot easily change constructors: events in the Drupal\elasticsearch_connector\Event namespace, and Elasticsearch query-construction objects in the Drupal\elasticsearch_connector\SearchAPI\Query. I propose we leave these more-complex cases out of this issue.

Proposed resolution

Where possible, remove constructors in favor of setting properties in \Drupal\Core\Plugin\ContainerFactoryPluginInterface::create in production and test code (but don't do this in the Drupal\elasticsearch_connector\Event nor Drupal\elasticsearch_connector\SearchAPI\Query namespaces).

Make empty constructors more-compact across the whole project.

Remaining tasks

1. Merge request 9.0.x - merge request !215 created by @mparker17 in #2
2. Merge request 8.0.x - merge request !216 created by @mparker17 in #4
3. Merge to 9.0.x - merged by @mparker17 in #6
4. Merge to 8.0.x - merged by @mparker17 in #8
5. Release 9.0.x
6. Release 8.0.x

User interface changes

None.

API changes

None.

Data model changes

None.