fix(eslint-plugin): [unbound-method] handling of logical expr

[bradzacher]

Fixes #1425

• Refactored tests. Having all of the tests is super hard to understand when one fails.
• The rule previously allowed true && instance.unbound, which is obviously not right.

Looking into it, there's 3 logical expressions: ||, && and ??.

• || and ?? both will return either the left or right expression.
• && will always return the right. Or rather, it can only return the left if it's falsy.
  • This means that const x = instance.unbound && something is safe, but const x = something && instance.unbound is not safe.

[typescript-eslint]

Thanks for the PR, @bradzacher!

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 #1440 into master will decrease coverage by 0.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #1440      +/-   ##
==========================================
- Coverage   94.45%   94.44%   -0.02%     
==========================================
  Files         142      142              
  Lines        6083     6085       +2     
  Branches     1728     1730       +2     
==========================================
+ Hits         5746     5747       +1     
  Misses        183      183              
- Partials      154      155       +1

Impacted Files	Coverage Δ
packages/eslint-plugin/src/rules/unbound-method.ts	94.44% <80%> (-2.62%)	⬇️