:active pseudo-class is applied to ancestor chain on mousedown

[LuckerCracker]

When clicking an element, :active is set on every ancestor in the event chain, not just the actual target element.

Steps to reproduce

1. Run rmlui_sample_demo.
2. Click any interactive element.

Expected behavior
Only the clicked element should receive :active (target phase).

Actual behavior
All ancestors receive :active as the event bubbles.

Root cause (code)
Element::ProcessDefaultAction() sets :active on mousedown without checking event phase.

Proposed fix
Only set :active for EventPhase::Target on EventId::Mousedown.

[mikke89]

Hi. This is indeed the current behavior for some of the pseudo classes, also including hover and focus. We diverge from CSS here for some good reasons.

We will need some bigger changes if we want to converge to the CSS behavior. For example, for a range slider. We want the pseudo classes to apply to the input element itself, but also need some way to adjust the looks of individual parts of an input which is active. This would be much more tricky with the CSS behavior with only one element active. With the current behavior we can easily style this as the pseudo class propagates up. I have some long-term features to address this, but nothing directly being planned.

Thus, for now we will keep this behavior. However, I've updated the documentation to describe this behavior for all the relevant pseudo classes (not just for :focus): mikke89/RmlUiDoc@e81414b

By the way, for the future. You don't have to push the issues through an LLM. Describing them in your own words is much preferred. Both for conciseness, for better understanding what you emphasize, and for the value of the human interaction itself - I don't want to talk to robots all day.