text-selection has too much height in spans with relative positions

[Milan Hauth]

minimal example:

```html

<div>
 <span>1</span>
 <span style="position: relative; top: 2em">2</span>
</div>

```

https://milahu.github.io/chromium-discuss-text-search-absolute-position-spans/issue4.html

complex example:

https://milahu.github.io/chromium-discuss-text-search-absolute-position-spans/test2.html

reproduce:

select text in spans with relative positions

actual:

text-selection highlight has too much height

above the selected text

in spans with relative positions.

the text-selection highlight

starts at the relative position y=0

expected:

text-selection highlight should have the same height

as with selected text in spans with absolute positions

this fails in chrome 137.0.7151.119

this works in firefox 139.0.4-1

use case:

EPUB-FXL = fixed-layout EPUB