Make "Open referenced file" more accessible

[bmuskalla]

Is your feature request related to a problem? Please describe.
When dealing with qlref files (especially in tests), i want an easy way to navigate to the referenced ql file. In the Explorer, this can be achieved by using the Open referenced file command when selecting a qlref file.

Describe the solution you'd like
I think the current feature is not very accessible as it's pretty well hidden and does not follow usual UX patterns found in VS code. The following are some ideas how to solve this (ordered by value)

• With a qlref file open in an editor, ability to navigate to the ql file within the editor (click the link/Go To Definition command)
• Ability to use the command on a selected qlref file in the Test Explorer (currently errors out)
• Ability to use the command on an open qlref file

Describe alternatives you've considered
An alternative may be to (at least of the test usecase) to not even show the qlref as a node in the Test explorer but insert access to the resolved ql file.

[mgsium]

Created a separate issue (#970) for this due to its complexity

• Ability to use the command on a selected qlref file in the Test Explorer (currently errors out)