Add template types to Result

[paulbalandan]

Description
Make ResultInterface a generic type.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

I think if the code is return $this;, the phpdoc should be @return $this.

$this: the element to which this type applies is the same exact instance as the current class in the given context. As such, this type is a stricter version of static, because the returned instance must not only be of the same class but also the same instance.
https://github.com/php-fig/fig-standards/blob/master/proposed/phpdoc.md

But if we can set return type, it should be static (or self).

[MGatner]

This one can be added at any point as a bugfix/tech-debt change so no need to rush it for 4.3.

[MGatner]

Looks good! Lots more baseline cleanup, makes me happy 🤗