fix(experimental-utils): simplify eslint-utils' findVariable's signature in ast-utils

[MichaelDeBoey]

https://eslint-utils.mysticatea.dev/api/scope-utils.html#findvariable

[typescript-eslint]

Thanks for the PR, @MichaelDeBoey!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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[codecov]

Codecov Report

Merging #3574 (678b15a) into master (84fff35) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3574      +/-   ##
==========================================
- Coverage   92.64%   92.52%   -0.12%     
==========================================
  Files         326      187     -139     
  Lines       11253     8393    -2860     
  Branches     3171     2580     -591     
==========================================
- Hits        10425     7766    -2659     
+ Misses        368      261     -107     
+ Partials      460      366      -94     

Flag	Coverage Δ
unittest	92.52% <ø> (-0.12%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...-utils/src/ast-utils/eslint-utils/scopeAnalysis.ts	100.00% <ø> (ø)
packages/scope-manager/src/scope/FunctionScope.ts
...ges/typescript-estree/src/create-program/shared.ts
packages/typescript-estree/src/node-utils.ts
...kages/scope-manager/src/scope/FunctionTypeScope.ts
...ckages/scope-manager/src/referencer/TypeVisitor.ts
packages/scope-manager/src/referencer/Reference.ts
...ckages/typescript-estree/src/jsx/xhtml-entities.ts
packages/scope-manager/src/lib/es2017.ts
packages/scope-manager/src/variable/index.ts
... and 130 more

[bradzacher]

thanks!