Deprecate VersionAwarePlatformDriver and ServerInfoAwareConnection

[morozov]

Q	A
Type	deprecation
BC Break	no

Currently, there are two ways the wrapper Connection can instantiate an AbstractPlatform:

1. If the driver is VersionAwarePlatformDriver, use:

   dbal/src/Connection.php

   Line 357 in b38ee5e

   return $this->_driver->createDatabasePlatformForVersion($version);

2. Otherwise, fall back to:

   dbal/src/Connection.php

   Line 360 in b38ee5e

   return $this->_driver->getDatabasePlatform();

Although these two approaches are mutually exclusive, version-aware drivers have to implement both methods. Additionally, there is an assumption that the driver connection used by all VersionAwarePlatformDrivers is ServerInfoAwareConnection which isn't enforced statically and requires runtime type checks assertions.

Whether or not the driver instantiates a platform based on the server version should be considered an implementation detail which may change when the support of a new platform version is added or removed. For instance, as of #3756, the SQL Server drivers do not use the server version to instantiate the platform but the connection is still declared as aware of the server version.

This detail doesn't need to be exposed outside of the driver and doesn't deserve an API.

[greg0ire]

Are there easy ways to write tests for this?