Remove the no longer needed error suppressions

Deprecate ServerInfoAwareConnection#requiresQueryForServerVersion() as an implementation detail

Deprecate PingableConnection in favor of handling lost connection

Update Slevomat Coding Standard to 6.3.10

Deprecate ExceptionConverterDriver

Fixes for the recently introduced driver-level deprecations

Update PHPStan to 0.12.31

Remove ServerInfoAwareConnection#requiresQueryForServerVersion() as an implementation detail

Testing the implementations of this method requires partial mocking of the implementing class which makes it impossible to make them `final` (#3590).

Additionally, this API breaks the encapsulation of the driver layer: instead of exposing the fact of whether the connection will perform a query to detect the server version, the driver should just instantiate a platform corresponding to a connection.

The rationale behind introducing this method (#487) is really questionable:

> This is also required for drivers that cannot return the database server version without an additional query (performance reasons).

1. There's no evidence that an underlying driver that exposes the server version via its API doesn't make a request of any kind to the server.
2. For an application that works with any realistic database, a query like `SELECT VERSION()` wouldn't be a performance bottleneck.
3. Even if it was, it's always possible to specify the platform version upfront. Otherwise, the current logic of falling back to a default platform may cause undefined behavior of the application (we don't test the compatibility of the lowest level of the DBAL platform with all supported server versions). Remember, “If it doesn’t work, it doesn’t matter how fast it doesn’t work.”

Preparation to marking OCI8 driver classes final

Remove DriverException::getErrorCode()

Deprecate DriverException::getErrorCode()

Mark non-interface OCI8 driver methods internal

The existing relationship between the connection and its statement violate the ISP principle. Instead of having access only to the execution mode of the connection, statements have access to the entire connection API.

Having a method which is not defined in the driver connection interface makes it impossible to mark the method `final` (#3590).

UPGRADE: Fix misplaced backtick

Remove the suppressed errors that PHPStan no longer reports