Add jasmine helpers and run their specs

What does this MR do?

Adds jasmine helpers, so we can start to store complex stubs and shared examples.

---

The new ClassSpecHelper is a helper for testing the structure of a class. It currently just has itShouldBeAStaticMethod which will assert that the provided base class and method name refers to a static class method.

For example:

describe('SomeClass', () => {
    describe('.someMethod', () => {
         ClassSpecHelper.itShouldBeAStaticMethod(SomeClass, 'someMethod');

         it('should have some other property to assert', () => { ... });
    });
});

Also see !6764 (merged) and !8412 (merged) for usage.

---

It also enables teaspoon to run specs for spec/helpers. For example, spec/javascripts/helpers/class_spec_helper.js and have the spec spec/javascripts/helpers/class_spec_helper_spec.js, which should be tested for coverage.

---

The .eslintrc update allows us to have branched dupes, but not block dupes.

For example, we can now do:

describe('SomeClass', () => {

    describe('.someMethod', () => {
        it('returns true', () => { ... });
    });

    describe('.someOtherMethod', () => {
        it('returns true', () => { ... });
    });

});

This wasn't possible before.

You still cant do:

describe('SomeClass', () => {

     it('returns true', () => { ... });

     it('returns true', () => { ... });

});

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Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #26305 (closed)