Alternate mod dirs for validation and manual installs

[HebaruSan]

Problem

In KSP-CKAN/KSP2-NetKAN#84, the validation script happily installed files to BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace and didn't complain:

https://github.com/KSP-CKAN/KSP2-NetKAN/actions/runs/5967777987/job/16190169201

There's a "GameData within GameData" validator in Netkan that catches the equivalent issue for KSP1.

Cause

The "GameData within GameData" check is hard-coded to use the string GameData.

Changes

• Now IGame.AlternateModDirectoriesRelative defines an array of strings specifying alternative locations where mods can be installed
  • This contains BepInEx/plugins for KSP2 and nothing for KSP1
• Now we scan both the primary and alternate mod dirs for manually installed DLLs
• Now the "GameData within GameData" checks the primary and alternate mod dirs, which makes it work for the above case:

$ netkan.exe --game KSP2 NetKAN/QuestariaAereospace.netkan
88958 [1] WARN CKAN.NetKAN.Transformers.SpaceWarpInfoTransformer (null) - Dependencies from swinfo.json missing from module: lfo
90045 [1] FATAL CKAN.NetKAN.Program (null) - BepInEx/plugins directory found within BepInEx/plugins:
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/addressables/AddressablesLink/link.xml
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/addressables/catalog.json
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/addressables/settings.json
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/addressables/StandaloneWindows64/defaultlocalgroup_unitybuiltinshaders_7891cbe984cbeb1f2d1f8278873f00dc.bundle
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/addressables/StandaloneWindows64/questariaaerospace_assets_all_9f16c5859564ddf24dd943dd94e9b57a.bundle
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/assets/plumes/BE-4.json
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/assets/plumes/IQNTR.json
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/assets/plumes/IQparrotEngine.json
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/localizations/english.csv
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/QuestariaAerospace.dll
BepInEx/plugins/QuestariaAerospace/BepInEx/plugins/QuestariaAerospace/swinfo.json

[techman83]

Looks great, thanks @HebaruSan !