RichTextLabel doesn't count wrapped lines properly

[KoBeWi]

Godot version:

3.2.3 rc3

Issue description:

This code

func _process(delta: float) -> void:
	if $RichTextLabel.visible_characters < $RichTextLabel.text.length():
		$RichTextLabel.visible_characters += 4
	
	print("Lines visible: ", $RichTextLabel.get_visible_line_count())

will always print 1 for a long text with multiple wrapped lines. It used to show the number of lines correctly.

This is a regression from #40217
CC @theoway

(adding 3.2 milestone because it's a cherry-picked regression, but the issue exists on master too)

Minimal reproduction project:
ReproductionProject.zip

[theoway]

I'll look into it.

[theoway]

I'll look into it.

Actually it doesn't count wrapped lines at all. It only counts lines and newlines that are drawn and are visible. As for before the fix, it wouldn't always give the correct number of wrapped visible lines.

[akien-mga]

I reverted the cherry-pick in 3.2 for now until we figure out the regression, so putting on the 4.0 milestone (where the regression is still present).

[akien-mga]

Seems reproducible in the current master branch (so it was not fixed by @bruvzg's RichTextLabel refactoring).

[bruvzg]

For the reference get_line_count and scroll_to_line functions do not count wrapped lines as well, so get_visible_line_count is consistent with other functions.