ui.log scroll-to-bottom working in ui.tab_panel

[evnchn]

Motivation

Fix #5118, where we find #5112 (or, actually, the reimplementation of it in 3.0, since we do q-scroll-area for ui.log) does not work inside ui.tab.

Implementation

I did 2 things:

• Act, only when document.body.contains(this.$refs.qRef.$el) (aka only when body contains the element, which is false when the ui.log hidden due to inactive in ui.tab_panel
• Go back to scrollTop + clientHeight >= scrollHeight approach for checking current scroll but we do it on this.$refs.qRef.$el.childNodes[0] this time around.
  • This I not sure but I think getScroll().verticalPercentage isn't accurate while ui.tab_panel under animation effect.

Progress

• I chose a meaningful title that completes the sentence: "If applied, this PR will..."
• The implementation is complete.
  • @falkoschindler Please do look at this, I am unsure.
• Pytests are not necessary.
• Documentation is not necessary.