[no-loop-func] New false positive in 4.0.0 when using a global type in a function in a loop

[lencioni]

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have read the FAQ and my problem is not listed.

Repro

{
  "rules": {
    "no-loop-func": "error"
  }
}

let someArray: MyType[] = [];
for (let i = 0; i < 10; i += 1) {
  someArray = someArray.filter((item: MyType) => !!item);
}

It is important here that the type is defined globally for the project in a different file. If the type is defined in the same file, the problem does not appear.

Expected Result

no-loop-func does not report an error

Actual Result

no-loop-func reports the following error:

Function declared in a loop contains unsafe references to variable(s) 'MyType'.

Additional Info

Versions

package	version
@typescript-eslint/eslint-plugin	4.0.1
@typescript-eslint/parser	4.0.1
TypeScript	3.9.3
ESLint	7.7.0
node	12.16.2

I suspect this could be related to #2039 maybe?

[bradzacher]

I didn't even know that rule used scope analysis! I missed it during my analysis of the ESLint codebase.

This looks like a problem because the base rule assumes that global variables are mutable.
We can extend this rule into this project and add support for ignoring type locations.

Doing a quick test, the only case that I can see wherein this rule will false-positive is for global types. Types with a declaration in the file (imported or otherwise) will correctly be identified as readonly and thus the rule will ignore them.