Add tests for binding value correctness

Some frameworks seem to sometimes modify values when they're set on the DOM for some reasons.

For example, Vue seems to convert `null` to `0` if the property was previously a number. This means that an element can't reliably use `null` and numbers together for the same property. See https://github.com/vuejs/core/issues/14209

Each framework that messes with values like this probably has its own set of edge cases, so we don't want to add a super-specific test like "sets a property to null when it was previously a number", and then one for each other edge case we find, but we have one test that bundles together all the edge cases that we find and runs them past each framework. At least until we get test weighting and can weight edge cases as lower than say, being able to set properties at all.