Add default actions extension point

[kulmann]

Description

This PR adds another extension point for the default actions of files (as used in resource table / tiles, etc). With this e.g. the new Open in Notebooks jupyter extension can be connected to the left click in the files list.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests
• Documentation
• Maintenance (e.g. dependency updates or tooling)

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[JammingBen]

Not for the scope of this, but what I noticed: shortcuts should probably be <a> links too, no? At least for a11y reasons.

[JammingBen]

Suggested change

	return unref(systemActions).filter(filterCallback)[0]
	return unref(systemActions).find(filterCallback)

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[kulmann]

Not for the scope of this, but what I noticed: shortcuts should probably be <a> links too, no? At least for a11y reasons.

It should be, but that would mean that we need to read and evaluate the .url files contents upon listing them, doesn't it?