Refactor OC\Server::getDatabaseConnection

[summersab]

This PR refactors the deprecated method OC\Server::getDatabaseConnection and replaces it with OC\Server::get(\OCP\IDBConnection::class) throughout the entire NC codebase (excluding ./apps and ./3rdparty).

Additionally, where necessary, the \OCP\IDBConnection class is imported via the use directive.

[ChristophWurst]

Suggested change

	$this->connection = \OC::$server->get(IDBConnection::class);
	$this->connection = \OCP\Server::get(IDBConnection::class);

let's use the public server container API. same applies to most changes below

[summersab]

I forgot to make this change before pushing, and I'm currently running tests locally. I don't know if you can cancel the tests that are currently running to free up resources, but feel free.

Also, why the change to the public container? In general, when should this be used?

[nickvergessen]

In general, when should this be used?

In new code: always
In old code: when you touch it anyways

[summersab]

I'm getting the following failure:

1) OCA\DAV\Tests\unit\Connector\Sabre\FilesReportPluginTest::testPrepareResponses
Failed asserting that null matches expected 200.

./server/apps/dav/tests/unit/Connector/Sabre/FilesReportPluginTest.php:445

Since this has to do with the dav app and not the core, how should I address this? I DO plan to refactor apps once my PRs for the core are approved. This seems a bit like a chicken and egg situation.

[skjnldsv]

Too much conflicts, closing until this is done fresh again