DBAL-1106 DBAL-1106 #768 Improve schema introspection performance on Oracle

[doctrinebot]

Jira issue originally created by user @doctrinebot:

This issue is created automatically through a Github pull request on behalf of deeky666:

Url: #768

Message:

This PR improves the overall schema introspection performance on Oracle by optimizing some of the getList*() method SQL queries in the platform.
Unfortunately Oracle system views are rather slow, especially when joining tables. Using subqueries can improve the execution time a lot.

_Improved queries_

(the times have been measured using an exemplary query from the functional test suite)

getListTableForeignKeysSQL(): Down from <sub>2.33s to </sub>0.68s per query
getListTableColumnsSQL(): Down from <sub>0.49s to </sub>0.14s per query
getListTableIndexesSQL(): Down from <sub>0.5s to </sub>0.25s per query

Overall improvement of OracleSchemaManagerTest from <sub>100s to </sub>37.5s.

I was quite impressed by the performance improvements :)

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-768] was assigned:
#768

[doctrinebot]

Comment created by @doctrinebot:

A related Github Pull-Request [GH-768] was merged:
#768

[doctrinebot]

Issue was closed with resolution "Fixed"

[github-actions]

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