Bootstrap 5 includes the following CSS on the page:
```css
*,
*::before,
*::after {
box-sizing: border-box;
}
```
That threw our `reliableTrDimensions` support test off. This change fixes the
support test and adds a unit test ensuring support test values on a page
including Bootstrap 5 CSS are the same as on a page without it.
Fixes gh-5270
Closes gh-5279
Ref gh-5278
