Fix enabling of dependencies with identical names

[TurkeyMcMac]

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• Goal of the PR
  • Fix the following situation: Mod A depends on mod B. There are two mods named B. The B mod earlier in the list is already enabled. When the A mod is enabled, the second B mod is enabled due to the dependency, leading to both B mods being enabled at once. This is incorrect. Since the first B mod is already enabled, it should be used to fulfill the dependency.
• How does the PR work?
  • When mod names are being mapped to indices, the indices of already enabled mods take precedence over others.
• Does it resolve any reported issue?
  • Not that I can find.

To do

This PR is Ready for Review.

How to test

1. Download and unzip mods boofarf.zip and foobarf.zip. boofarf depends on foobarf.
2. Put the mods into your mod directory. Put foobarf in twice using a symlink.
3. Try enabling boofarf with neither foobarf enabled. The one later in the list should become enabled.
4. Disable boofarf and both foobarfs.
5. Enable the first foobarf listed.
6. Try enabling boofarf. The first foobarf should remain the only one enabled.