Core: Replace entity ptr for WideScanTarget with EntityID_t

[zach2good]

I affirm:

• [x] I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
• [x] I understand I should leave resolving conversations to the LandSandBoat team so that reviewers won't miss what was said.
• [x] I have read and understood the Contributing Guide and the Code of Conduct.
• [x] I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Replaces: https://github.com/LandSandBoat/server/pull/6392

The previous PR became a staging ground for me testing entity lookup. This is the minimum amount of work for this ptr replacement.

[zach2good]

Tested, working with setting a widescan target, seeing them on the minimap, zoning and then your set target isn't set anymore, etc.