Rethink how to handle a[href] > button cases

The following scenario fails the `target-size` rule. Axe-core allows nested controls inside links, because the HTML spec does as well. But in a scenario like this where the button is the only content of the link, and the target area is almost the same I think we can reasonably conclude this should fail the `nested-interactive` rule rather than the `target-size one:

## Expected

Axe-core report the following as a `nested-interactive` issue, rather than a `target-size` issue.

```html

Click me

```

Start by locating the target-size and nested-interactive rule entry points and their tests, then reproduce the provided link-and-button HTML case. Done means this markup is reported as a nested-interactive issue rather than a target-size issue, with the existing rule tests still passing.

Written by the indexing model from the issue text.