Use the largest ascent as the ascent for a font

[emilk]

• Closes Improve vertical centering of text (e.g. in buttons) #4929
• Builds on top of Improve vertical alignment of fonts #2724 by @lictex (ptal!)

I think we need both this and some sort of centering (like in #5117) – I'll experiment more. Maybe we should to take the FontImpl ascent and the Font ascent into account when centering 🤔

[lictex]

egui/crates/epaint/src/text/font.rs

Lines 355 to 359 in f4ed394

	let pixels_per_point = fonts[0].pixels_per_point();
	let row_height = fonts[0].row_height();
	let mut slf = Self {

egui/crates/epaint/src/text/font.rs

Lines 422 to 426 in f4ed394

	#[inline(always)]
	pub fn row_height(&self) -> f32 {
	self.row_height
	}

row height should be taken from the same font as the ascent, otherwise rows could be clipped vertically.
doing this will make all rows higher but text should be naturally centered again then.

imo whether to use metrics from the primary font (font[0]) or the largest font is more like a design choice that, is the fallback font important enough to massively affect the layout process?

probably offtopic:
FontTweak::baseline_offset_factor (used to manually shift rows as a last resort) is getting a bit confusing. maybe it should be moved to Font instead

[emilk]

I've returned to a mixed approach in #5117 now - it seems to work very well (finally!)