Usability improvements for missing files

[HebaruSan]

Problem

Discord user dan reported frequent prompts from the dev build to reinstall mods after running the game, which said "metadata changed" even though the metadata for those mods had either never changed or changed over two years previously:

Cause

This turned out to be due to ZeroMiniAVC, which deletes files that CKAN installed. The feature from #4067 detects that as a mod with missing files and prompts the user to reinstall that mod.

This was challenging to figure out for a CKAN developer and a dev build power user. It should be understandable for anyone.

Changes

• Now if a reinstall is due to a missing folder or file, the change reason says "Re-install (missing folders or files)"
• Now the Contents tab shows missing folders and files in red, with a "Folder not found!" or "File not found!" tooltip, and scrolls to the first one when there are any
• Now the Contents tab shows empty folders (previously hidden)
• Now the Contents tab hides paths that are matched by the installation filters from Global install filters #3458 (previously shown)
• Now the Contents tab's double-click-to-open-in-file-explorer feature works more reliably when CKAN isn't started from the game folder

This way if someone encounters this after the next release, we can tell them to click the changelog entry, then the Contents tab, and the missing file will be apparent immediately.

Separately, KSP-CKAN/NetKAN#10230 is updating ZeroMiniAVC's metdata to direct users to the CKAN setting they should be using instead.