[pgAdmin4][RM3936] Feature tests failing intermittently for SQLeditor related test cases

Hi Hackers,

Attached is the patch to fix failing SQL editor related feature tests.

The failure is occurring mostly because of send_keys function of selenium which sometimes does not input the complete text. The change will use Codemirror javascript object to set the text.

I have also added new args flag "--modules" which can be used after --pkg where you can test a specific module file under the pkg. This is not so useful for build but definitely helpful for the developers.

Kindly review.