To reduce time spent on the splash screen, recent changes skip
refreshing the online mod list if older version is found in IndexedDB
cache. This means the user might have outdated mod list when importing
a profile, and the manager can't import mods it doesn't know about. To
mitigate the issue, a warning was added to profile preview step with an
option for the user to update the mod list.

However, the warning uses the mod list in Vuex to check if a mod is
available, which is a mistake since that only checks if the mod itself
is known, and not whether the mod version in the profile is known. This
caused recently updated mods to not always trigger the warning. The
download part uses IndexedDB as its source of truth, and silently
ignored the unknown mods/versions, since user has explicitly decided to
import a partial profile.

To fix the issue, both parts now use IndexedDB as the source of truth.

The implementation in ImportProfileModal now somewhat akwardly handles
the mod information as ExportMods (read from mods.yml and required to
know which mods are disabled), ThunderstoreMods (required to use
existing UI components), and ThunderstoreCombos (required to download a
specific version of the mod). This could potentially be simplified but
is outside the scope of this PR.

ExportMod support was dropped from TsModsModule functions to remove the
footgun that caused this whole problem.