extract loadPreview into helper

[fschade]

Description

in the past loadPreview only was needed from within vuex store, with the upcoming preview feature and search // filter it is required to be able to use preview loading outside the store too. This pr utilize loadPreview and make it available as a helper.

Related Issue

• required for [full-ci] Search and filter #5415
• required for "Details" in the Sidebar #5161

Motivation and Context

extract more and more logic out of vuex

How Has This Been Tested?

• local installation and unit tests
• ...

Screenshots (if appropriate):

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

Checklist:

• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

Open tasks:

[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.

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

87.5% Coverage
0.0% Duplication

[ownclouders]

Results for oCISSharingBasic https://drone.owncloud.com/owncloud/web/16974/47/1
The following scenarios passed on retry:

• webUIRestrictSharing/restrictSharing.feature:49

[ownclouders]

Results for oC10Basic https://drone.owncloud.com/owncloud/web/16974/6/1
The following scenarios passed on retry:

• webUIPreview/imageMediaViewer.feature:35

[pascalwengerter]

Lovely!