feat(prefer-mock-return-shorthand): greatly improve checking if mutable variables are used (#1914)

* test(prefer-mock-return-shorthand): add more cases

* refactor(prefer-mock-return-shorthand): move mutability checker into a function

* fix(prefer-mock-return-shorthand): check shallow objects for use of mutable values

* fix(prefer-mock-return-shorthand): check shallow arrays for use of mutable values

* fix(prefer-mock-return-shorthand): handle binary expressions

* fix(prefer-mock-return-shorthand): handle nested nodes

* fix(prefer-mock-return-shorthand): support function arguments

* fix(prefer-mock-return-shorthand): support member expressions

* fix(prefer-mock-return-shorthand): support spreading

* fix(prefer-mock-return-shorthand): support bitwise and unary operators

* fix(prefer-mock-return-shorthand): support optional chain expressions

* fix(prefer-mock-return-shorthand): support logical expressions

* refactor(prefer-mock-return-shorthand): use fallthrough

* fix(prefer-mock-return-shorthand): support new expressions

* fix(prefer-mock-return-shorthand): check computed properties

* fix(prefer-mock-return-shorthand): check conditional expressions

* refactor(prefer-mock-return-shorthand): simplify checks

Author: G-Rath