Remove shrink ray from TopicsPage content side panel

[nucleogenesis]

Summary

Fixes #9347 wherein the View Resource link from the metadata side panel on the Topics page would cause the content you navigate to being shrunken and squeezed.

The issue was that in order to avoid the content underneath the side panel scrolling when scrolling within the modal side panel, we watch the value that triggers the opening of the modal. In that watcher, it sets the html.style.position to 'fixed', which remains through router navigation and caused the entire tag to be smushed.

The fix was to unset it in the beforeDestroy hook in TopicsPage - I added some comments to explain the behavior.

References

Fixes #9434

Reviewer guidance

Go to a Topics page, open a content item's side panel, click "View Resource" and see the content in the expected form.

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Testing checklist

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Reviewer checklist

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[marcellamaki]

Looks good! Thanks @nucleogenesis