DiffGenerator: fix removing schema from table name before applying regex filtering

[cristi-contiu]

Q	A
Type	bug
Fixed issues	#1487

Summary

Failing test and suggested fix for #1487, requested in https://github.com/doctrine/migrations/pull/1490#pullrequestreview-2645902823

There are differences in the way Migrations and DBAL apply the SchemaAssetsFilter, usually regex: DBAL applies it on the table name (which can be qualified or unqualified, depending on platform schema support and if the table is in the default search-path schema) while Migrations always removes the schema and only applies the filter on the unqualified table name (my_table).

This fix applies the SchemaAssetsFilter on the table name exactly as provided by the DBAL for platforms that support schema.