Wrap instance reporting for database schema in an API

[miaulalala]

Problem

Currently, we're checking for the Database Type of an instance something like this:

$schema->getDatabasePlatform() instanceof PostgreSQL94Platform

If we ever change the underlying structure, these checks might break.

Proposed solution

Add a new API method for ISchemaWrapper that will return the database type as a string and a few constants that map to the supported databases to compare the Database string too:

public CONST PostgreSQL94Platform = 'PostgreSQL94Platform';
....

public function getDatabaseType(): string;

Context

[ChristophWurst]

I'd rather put this onto \OCP\IDBConnection to make it also usable outside the context of migrations.

This will be a solid replacement for the leaky \OCP\IDBConnection::getDatabasePlatform. Ref

server/lib/private/DB/ConnectionAdapter.php

Line 194 in 34f425c

* @todo we are leaking a 3rdparty type here