Fix debug toolbar db connection count

[danielTiringer]

Fixes #5160

Description
The debug toolbar's database tab showed X queries 0 connections - the count of used connections was not reported.
The change counts the unique (name) connections while iterating through the queries, and saves them in a new static variable. Then this variable is used to display the count.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[lonnieezell]

It looks like it's already trying to count the connections that it finds in the constructor. Have you verified what is going wrong there?

[danielTiringer]

It looks like it's already trying to count the connections that it finds in the constructor. Have you verified what is going wrong there?

It seems to me that the toolbar's Database collector is created before a database connection is made. Its constructor gets the connections from the config, but at that time, nothing's connected and an empty array is returned.
If we do the getConnections() call at the start of the getTitleDetails() function, the connection is returned as expected.

That can be an alternative too, refreshing the connection array.

[lonnieezell]

Ah - good point. I think doing a getConnections() at the start of getTitleDetails() as you've mentioned works well. That doesn't have us keeping duplicate info around.

[danielTiringer]

Ah - good point. I think doing a getConnections() at the start of getTitleDetails() as you've mentioned works well. That doesn't have us keeping duplicate info around.

Alright, changed the PR accordingly.

[lonnieezell]

Looks good. Thanks!